Tom frowned. "I'll organize a search right away. Where are you calling
from?"

"Police headquarters at Sandbank."

"Okay. Take it easy, and I'll send a whirlybird to pick you up," Tom
promised.

"And don't forget some clothes," Bud added with a chuckle. "Mel and I
are getting chilly."

"Right!" Tom hung up and gave Arv Hanson a quick briefing.

Then he phoned the base airfield to dispatch a helicopter. He also
contacted the nearest Coast Guard station and put through a
long-distance call to Navy Headquarters in Washington to request help in
searching for the jetmarine. Finally he and Arv headed back to the
submarine docks in the jeep.

A flurry of activity followed as Tom detailed ships for the search and
rounded up crews. He was interrupted by a phone call in the loading
shed. It was the control-tower operator.

"One of our drone planes has spotted a sub approaching, skipper," the
operator reported.

"What bearing?" Tom demanded excitedly.

"One-seven-six." Tom was about to hang up and grab a pair of binoculars
when the operator added hastily, "Wait! It's responding to our radio
challenge!... That's ours, all right!"

Tom dashed out of the shed and scanned the sea to the southward. Sure
enough, a jetmarine had surfaced and was speeding toward the sub docks.
Minutes later, Tom was shaking hands warmly with Zimby Cox and Mack
Avery.

"Is Bud okay?" was Zimby's first question.

"Right! I just heard from him," Tom replied. "He and Mel captured those
enemy frogmen and a copter's on the way to pick them up. What happened
to you fellows?"

Zimby confirmed Bud's guess that they had taken off in pursuit of the
enemy craft.

"We figured Bud and Mel could make out on their own," Zimby explained.
"And we thought the sub's course or actions might tip us off to its
nationality. Also, if it tried any sabotage or mine-planting, we could
radio the Navy."

Instead, Cox went on, the mysterious craft had proceeded to a point
about ten miles offshore where it rendezvoused with another submarine.

"And get this, skipper!" Mack Avery put in. "The other sub was
undetectable! We were close enough to get a peek at it, but we couldn't
ping it on the sonarscope."

"That figures," Tom said grimly. "Those frogmen were apparently
Brungarians."

Zimby Cox related that a man had transferred from the undetectable
submarine to the one they had been following. The first sub had then
headed out to sea, as if to cross the ocean back to its home base. The
other had departed on a course toward the South Atlantic.

"Probably back to the lost missile area. At least that's the way we
figured it," Zimby added.

"And neither sub spotted you?" Tom questioned.

Zimby grinned wryly. "We might not be here if they _had_ detected us.
But I'm pretty sure they didn't. Anyhow, they gave no sign."

Tom was doubly elated at the news. His antidetection gear had evidently
worked perfectly in a showdown test with the enemy, even at close range.
Moreover, if the second sub was returning to the South Atlantic, it
seemed likely that the enemy, too, had not yet located the precious
missile with its data from Jupiter.

"You guys rate Navy medals," Tom told Zimby and Mack jubilantly. "Come
on back to Shopton with me and I'll buy you the juiciest steaks in
town!"

Before leaving the base, Tom called the Coast Guard and the Navy to
cancel his search request. He also telephoned a full report on the enemy
submarines to Admiral Walter.

After hanging up, Tom decided on another move. "Our antidetection gear
seems to have panned out pretty well," he told Hank. "I think we should
make use of it right away. By sending that jetmarine to the South
Atlantic, we might get a line on enemy activities down there."

Hank was in favor of the idea. He volunteered to prepare the jetmarine
for a cruise and take off from Fearing that very night.

"Thanks," Tom said with a parting handshake. "Keep us posted if you
learn anything."

Meanwhile, Bud and Mel Flagler had arrived at the base by helicopter.
They and their two shipmates flew back to the mainland with Tom and Arv
for a celebration dinner in town.

The next morning found the young inventor hard at work in his private
laboratory. He was tapping his head with his slide rule and frowning at
a blackboard scrawled with equations when Bud dropped in for a visit.

"What now, inventor boy?" his copilot asked. "Don't you ever give that
brain of yours a rest?"

"Oh, hi, Bud!" Tom looked around absent-mindedly. "I'm just trying to
figure out a way to crack the Brungarians' antisonar system."

"Good night!" Bud sank down on a lab stool. "You've come up with a way
to make our own subs undetectable. Isn't that enough?"

Tom shook his head. "Not if we want to keep track of those sneaks. And I
think I see a way to do it."

"How?"

"So far, I have been thinking about refining our own search sonar." Tom
explained that the new system he had in mind would send out a _complex_
pulse--that is, an underwater sound wave with many harmonics instead of
a single tone, sharp-peaked sound impulse.

"This will make it less likely that their antidetection gear will absorb
all of it," Tom went on. "What's not absorbed will return as an echo.
I'm also going to modify our receivers. But I've still not worked that
out."

Bud nodded, his forehead puckered in a look of concentration. "So--?"

"So our sonar picks up all that hash, and by means of a computer setup
filters out the sub's real echo from the shadow reflections."

"Hey! Sounds pretty cute," Bud said.

Tom broke into a dry chuckle. "Right--_if_ I can do it." After that job,
Tom added, he hoped to adapt his own antidetection methods to make
hydrolung wearers safe from underwater detection. "And if the Jupiter
prober hasn't been found by that time, Bud, I'm going to request the
Navy to let us take over the search alone."

Bud gave a whistle of excitement at the possibility of new undersea
adventures ahead. "Count me in, pal!"

The two boys broke off their conversation a short time later and went
back to the Administration Building for lunch with Tom's father.

Mr. Swift greeted them with a smile as they entered the big double
office. "Glad you could join me, boys! Chow's laid out quite a feast for
us today."

Three places had been set at the conference table, and an appetizing
repast of sizzling ham and sweet potatoes waited in covered dishes on a
lunch cart nearby.

"Mmm!" Bud inhaled the aroma. "Good chow from good old Chow!"

Tom switched on the videophone screen to a private channel to catch the
noon news while they ate. The newscaster wore a look of excitement as he
spoke without pausing for the usual commercial.

"The Brungarian government has just scored a propaganda bombshell!" he
reported. "In a news announcement released less than half an hour ago,
they stated that their Navy has perfected an _undetectable submarine_!"

The Swifts and Bud froze, openmouthed, at the newscaster's words.

"No need to tell you what this could mean to American security," he went
on. "If enemy subs slipped through our continental defenses, their
missiles could devastate the United States with scarcely an instant's
warning! The whole country's been rocked by the announcement. An
official comment by our Defense Department is expected at any moment."

"Sufferin' satellites!" Bud gulped.

Mr. Swift nodded. "It's a great propaganda stroke. But I wonder why
they've chosen to reveal their secret at this time."

Tom said thoughtfully, "Dad, do you suppose they've realized the fact
that we _know_ about their antisonar gear?"

"Could be, son. They may figure that since the secret is out already,
they may as well play it up for all it's worth." The elder scientist
paused and frowned. "Or it might be intended to force our hand."

"You mean in hopes of getting us to reveal whether or not we have an
antidetection system ourselves?" As his father nodded, Tom scowled. "If
so, that sub yesterday may have been observing our tests."

The telephone rang and Tom leaped to answer it. The caller was Dan
Perkins of the _Shopton Evening Bulletin_.

"You can guess why I'm calling, Tom," the editor said. "How about a
statement from you Swifts on this Brungarian sub story?"

"We found it very interesting," Tom said politely but noncommittally.
Parrying further questions, he hung up as soon as possible.

Mr. Swift approved Tom's policy of silence. Almost immediately the phone
began ringing again with a succession of calls from other newspapers and
wire services. Tom dashed off a brief, general statement and instructed
Miss Trent to give it to all further callers.

"Maybe this is a good time to make a private announcement to you
fellows," Mr. Swift said to the two boys, his eyes twinkling. "Do you
recall my telling you that Doc Simpson had isolated an unknown vitamin
from the space plants? Well, we've now discovered that this vitamin can
condition the human body to stay under water indefinitely. Doc is
putting some up in capsule form."

Both Tom and Bud gave whoops of glee at this news.

"Dad, you've helped overcome one of the big problems in our search for
the lost missile!" Tom exclaimed.

CHAPTER XV

MOUNTAIN HIKE

"After adequate doses of your space vitamin, Dad, a skin diver could
tackle almost any undersea job in my hydrolung!" Tom exclaimed. "He
wouldn't be subjected to any antiosmosis troubles with his body
tissues."

His father nodded. "For the first time, man might become a _truly marine
creature_!"

"Wow! Think of it!" Bud gasped excitedly. "With Tom's hydrolung and a
knife to hunt his own food, he could practically live in the sea!"

"That's no farfetched dream, Bud." Tom's steel-blue eyes flashed at the
thought of new fields of scientific conquest. "This discovery of Dad's
and Doc Simpson's opens up some really amazing possibilities."

Most important at the moment, the vitamin would be a great boon in
carrying out search and digging operations for the Jupiter prober. With
fresh enthusiasm, Tom returned to his laboratory to work on the new
sonar gear. In his own mind, he had already named it a "quality analyzer
sonar," since that exactly described the way it would function.

"Hmm, let's see," Tom mused as he settled down at his workbench, pencil
in hand. "Besides a regular sonarscope, I'll need at least three units
for the gear."

First, he would need an oscillator to produce the complex pulse. Next,
of course, an oscilloscope to check the pulse as it was beamed out.
Last--but highly important--a correlation calculator.

This latter unit would compare the original pulse with the returning
echoes. If an echo had a high enough "standard of acceptance"--that is,
if its quality was very near the original pulse, it would show up on the
screen in the normal way. If the echo came back blurred, or if "shadow
echoes" showed up, these would be separated and appear on the screen
colored red.

"Whew!" Tom sighed as he realized the complicated job of circuit design
that lay ahead. "This sure is going to burn some midnight oil!"

The young inventor worked all afternoon at a furious pace, breaking off
toward dinnertime to telephone his mother that he would be staying
overnight at the lab. After a hasty meal, he resumed his layout job at
the drawing board and by midnight had finished designing his quality
analyzer sonar.

Whipping off his eyeshade, Tom went into the apartment next door and
stretched out to snatch a few hours' sleep. But as usual when in the
midst of an exciting new project, he was too keyed up to rest for long.

Before daylight, Tom was back at his workbench ready to begin assembling
the units of his new sonar gear. Later he phoned Chow but scarcely
paused to eat when the cook arrived with his order.

"Brand my solar stovepipe!" Chow scolded. "Take time to eat your vittles
properly, boss!"

"Hmm?... Oh, sure." Tom looked up and grinned.

The stout old Texan stomped out, shaking his head.

As the morning wore on, the pace at which Tom had been working began to
tell on the young inventor. His head nodded again and again. Gradually
he fell forward into an exhausted doze.

The next thing Tom knew, he was sailing through the air, high above
Swift Enterprises. Lake Carlopa was a tiny blue puddle below, and the
town of Shopton a mere cluster of toy buildings in the distance.

"Good grief!" Tom exclaimed with a gulp. "What's keeping me up?"

He was floating freely, without the support of any aircraft--or even one
of his amazing force-ray repelatrons!

The discovery triggered off disaster. Like a character in a movie
cartoon, now that he knew he had nothing to support him, Tom instantly
went plunging downward--down, down, straight into the lake!

_Splash!_

Tom gasped and shuddered and shook his head like a drenched terrier.

_Another splash!_ As Tom brought his eyes into focus, he realized he was
back at his workbench in the laboratory. Chow was standing in front of
him, holding a half-empty pail of water, ready to splash him again!

"Hey! Cut it out!" Tom cried out, jerking bolt upright. Then, as he saw
the disturbed look on Chow's face, Tom burst out laughing. "Okay. Relax,
old-timer! Guess I was dreaming."

"Brand my snake oil!" Chow said. "You looked so pale an' pasty, you had
me plumb scared, Tom! I couldn't wake you nohow!" Worriedly the cook
added, "What you need is a good beefsteak and some sunshine. You been
under water too long."

"In more ways than one!" Tom chuckled as he grabbed a towel and dried
himself off.

The beefsteak, with crisp golden-brown French fried potatoes, was
already at hand on Chow's lunch cart. Tom ate with a hearty appetite
and the stout chef went off, secretly plotting to arrange the second
half of his prescription.

When he reached the galley, Chow plucked the wall phone off its hook and
called Bud at an airfield hangar. After a brisk conversation, he hung
up, grinning contentedly.

At one o'clock Bud came bursting into Tom's laboratory. "Snap to,
skipper!" he announced. "You have company!"

Tom looked up from his work in surprise.

"_Ta-daaa!_" Bud sang out, imitating a trumpet flourish.

Sandy and Phyl Newton marched in, smiling.

"Boy, this _is_ a surprise!" Tom got up to greet them. "A mighty
pleasant one. But what's the occasion?"

"The occasion is that you're coming on a mountain hike with us, out in
the nice fresh air and sunshine!" Sandy informed him.

"And please don't argue," Phyl said with a giggle. "It's for your own
good--not to mention ours."

"I suppose Chow Winkler put you up to this." Tom grinned.

"Never mind that," Sandy said sternly. "Just come along quietly. It's a
beautiful day."

Tom glanced at his workbench cluttered with drawings and electronic
gear. "Well, okay, since you're twisting my arm," he agreed. "I guess it
might clear my brain at that."

"Now you're talking." Bud clapped Tom on the back and propelled him
toward the two girls, who promptly seized his arms before he might
change his mind.

On their way to the door, however, the telephone rang. Tom insisted upon
answering it, in spite of the girls' scolding.

"Tom Swift Jr. talking."

"This is Chief Slater, Tom," said the voice at the other end of the
line. "Dimitri Mirov wants to see you. I don't know what's up, but he
might be ready to tell something worth while. Could you drop by?"

"Sure thing, Chief. Right away!" Tom hung up, excited by the thought
that the Brungarian might be about to reveal an important secret. "Mind
stopping by police headquarters first?" he asked his friends.

Minutes later, Bud's red convertible pulled up in front of the gray
stone building. Tom jumped out and dashed up the granite steps.

"I've had Mirov transferred to a cell by himself," Chief Slater said as
he took Tom back to see him. "Figured he might talk more freely away
from his pals."

The prisoner, however, showed no eagerness to do so at Tom's arrival. He
remained slouched on his bunk as the young inventor pulled a chair up to
the cell bars. His only response was a slight curl of the lips.

"Have you heard about my country's new submarine?" Mirov inquired after
Chief Slater left.

Tom nodded curtly.

"When are _you_ going to build one?" Mirov prodded slyly.

"Look!" Tom snapped. "You asked to see me. Here I am. What is it you
want?"

Mirov shrugged with a look of amusement. "To make a bargain with you,"
he replied casually. "I know the secret of that sub. Get me and my
friends released and I'll give it to you."

Tom had no intention of doing so, but he parried the offer, hoping to
draw Mirov out further. The prisoner, however, would say nothing more.

At last Tom gave up and rose to leave. "I'll think over your
proposition," he said.

He heard Mirov chuckle as he walked away. Somewhat puzzled, Tom reported
the conversation to Chief Slater and also telephoned the plant to inform
Ames.

Then he hurried back to the car. Bud frowned upon hearing Tom's story.

"Do you think he's on the level?"

Tom shrugged as they headed out into the countryside. "I may be wrong,
but the whole thing sounded fishy."

"Now look!" Sandy said severely. "If we're going to enjoy this hike,
we're _not_ going to talk about Brungarians or inventions or that lost
missile. From now on, it will cost anyone five cents every time he
breaks the rule!"

The boys chuckled and agreed. But agreeing proved easier than keeping
the rule. Again and again, either Tom or Bud would inadvertently drop a
remark about their submarine experiments or the search in the South
Atlantic. By the time they had parked in the hills and started climbing,
Sandy's and Phyl's pockets were jingling with coins.

"What are you going to do with it all?" Bud asked jokingly.

"_Give it to us!_" snapped a strange voice.

As the four young people turned with a start, they saw two men burst
from the shrubbery just behind them.

Both were holding guns!

CHAPTER XVI

THE GUNMAN'S SURPRISE

Sandy and Phyl were terrified by the sudden appearance of the
rough-looking pair with their drawn revolvers. Tom and Bud remained
cool, eying the men warily.

"What's the big idea?" Tom asked.

"Shut up and hoist your mitts!" the bigger of the men snarled. As the
boys obeyed, he muttered to his partner, "Keep these two punks covered,
Mugs, while I take their cash!"

"Right, Packy! I'll watch 'em!"

Sandy and Phyl emptied their pockets. Then Packy took the boys' wallets
and change.

"Now turn around and march!" Packy snapped.

Bud took the lead, followed by the two girls, with Tom bringing up the
rear. They plodded up the brushy slope in silence for several minutes.
Presently a weather-beaten cabin in a grove of trees came into view.

"You intend to hold us there?" Tom asked.

"You'll find out soon enough!" Packy answered. "We'll teach you to
interfere with the Mirovs!"

_The Mirovs!_ Like pieces of a jigsaw puzzle, the whole picture suddenly
fell into place. It was clear to Tom now how the capture had been
arranged.

The call to the jail from Dimitri Mirov had been a hoax. Its purpose had
really been to get Tom away from Enterprises--thus giving the two thugs
a starting point from which to follow him. The mountain hike, organized
by Bud and the girls, had played right into their hands! As Tom sized up
the situation, seeking a way out, the group reached the cabin.

"What are your terms for letting us go?" Tom asked their captors,
stalling for time.

The man named Packy gave an ugly chuckle. "None yet," he said. "We may
just decide to set the cabin on fire."

Sandy uttered a gasp as his words sank home. Phyl Newton had turned
deathly pale. Packy now told his partner to unlock the cabin. Mugs
stepped to the door.

At that moment Tom caught Bud's eye. _It was now or never!_

Tom whirled and smashed a stiff handblow to Packy's wrist, knocking the
gun from his hand. Bud hurled himself on Mugs.

Taken off guard, the shorter thug staggered and went down under a hail
of punches. Bud grabbed his wrist and twisted it mercilessly while he
pinned him to the ground.

Mugs screeched with pain. "C-c-cut it out!"

"Then drop your gun!" Bud snapped.

Tom, meanwhile, had followed up his first advantage with a stunning blow
to the solar plexus. Packy grunted for breath, then came back viciously
with several well-aimed punches that staggered Tom.

As the young inventor stumbled backward, Packy dived for his gun. Though
still groggy, Tom managed to kick the weapon out of reach. Before Packy
could straighten up, Tom followed with a sweeping uppercut that caught
him squarely on the chin.

Packy went down like a felled tree!

Tom picked up the gun before his groaning victim could recover. By this
time, Bud had pounded his own opponent into submission. Within a few
moments, both thugs were lined up against the wall of the cabin. Their
wrists were tightly strapped behind them with their own belts.

"Oh ... thank goodness!" Sandy gasped.

Tom gave the girls a reassuring grin. "Are you two all right?"

"I g-guess so." Phyl gave a nervous smile.

Now that the tables were turned, it was the thugs' turn to "march."
The boys herded them warily back down the hillside toward the road,
where Bud had parked his red convertible. Sandy and Phyl followed close
behind.

[Illustration: _Tom and Bud hurled themselves at the thugs_]

Like all cars belonging to the Swifts' key personnel, Bud's was equipped
with a two-way shortwave radio. Tom switched it on and radioed Shopton
Police Headquarters. Chief Slater promised to send a squad car at once.

Minutes later, they heard it approaching. Two husky police officers
leaped out as the car braked to a halt, and took charge of the
prisoners. Scowling and sullen, they were driven off to jail.

"Well," said Bud jokingly, "what about that relaxing hike we were
starting?"

Phyl sighed. "I'm afraid you two boys just can't get away from
_in_ventions and _ad_ventures."

Sandy added, "I suggest we go home for a nice safe dinner."

Later, at the Swifts' house, Tom received a telephone call from Chief
Slater. He reported that the two prisoners were known hoodlums from a
nearby city.

"They claim they were hired for this job last night by a stranger who
spoke with an accent," Slater went on. "According to their story, they
never even got a look at his face, and they had no idea he was an enemy
agent."

"Sounds reasonable," Tom agreed. "It's not likely Mirov's Brungarian
henchmen would endanger their whole setup by taking any cheap gunmen
into their confidence."

Chief Slater also reported that Len Unger was still at large. "But the
FBI will probably pick him up soon," he added.

"I sure hope so," Tom said.

A ten-hour sleep that night proved a fine tonic. Tom awoke the next
morning feeling entirely refreshed, and after a hearty breakfast,
hurried off to the plant. Here he plunged into work on his quality
analyzer sonar.

Much of the circuitry was assigned to the electronics department. The
finished boards and sub-assemblies were fed back to Tom in his private
laboratory. He himself assembled the major units.

At lunchtime, over a bowl of chili and crackers, Tom recalled another
problem. "We'll need an undetectable sub to test my analyzer," he mused.
"That means a repeat job of rigging all those transducers. Whew! I'd
better get busy on that plastic sheathing."

As soon as he had eaten, Tom phoned Arv Hanson, who arrived at the lab
in a few moments.

"You remember that idea I mentioned to Danny about molding all the
transducers into a single continuous plastic sheet?" As Arv nodded, Tom
went on, "Let's try it, using Tomasite as the plastic."

Tom picked up a pencil and quickly sketched out the production steps.
By machine-spacing the transmitting and the receiving transducers as
closely together as possible, with minimum clearance, the plastic
coating could do an even better job of absorbing sonar pings than the
hand-rigged model.

"And the leads from all the transducers can be combined into a single
flat tape," Tom ended. "That'll make it simple to hook up with the
electronic control unit inside."

"Got it, skipper," Arv said tersely. "It'll take overtime to set up the
job in the plastics department. But we ought to be rolling out the
sheeting Tuesday."

"That's swell, Arv! Thanks!"

By midmorning Tuesday, Tom had his quality analyzer sonar completed and
was showing Bud how the units worked.

"Boy, it looks simple enough the way you explain it, prof!" Bud said
admiringly. "How soon can we try it?"

"Depends on Arv," Tom replied. He picked up the phone and called the
plastics department. To his delight, the sheathing was already being
rolled out in quantity. Arv promised that by noon he would have enough
of it available to coat a jetmarine.

"Nice going!" Tom said. "Shoot it out to the cargo-jet hangar as soon as
it's ready!"

Soon after lunch, Tom, Bud, and Arv took off for Fearing Island. When
they arrived at the base, the plastic coating with its myriad tiny
"mikes" and "speakers" was speedily applied to a jetmarine under Arv's
supervision. Tom, meanwhile, wired the control unit and also installed
the analyzer sonar in the _Sea Hound_.

"Want to be 'It' for another underwater game of hide-and-seek?" Tom
asked Bud with a grin.

"Sure, but don't tag me with a torpedo!"

Minutes later, the jetmarine slipped off into the depths with Bud and
two other crewmen aboard. Tom and Arv followed in the seacopter. The
quality analyzer sonar worked even better than Tom had hoped. He not
only tracked the jetmarine on its outward course, but located it three
different times after shutting off the analyzer long enough for Bud to
seek a new location.

"How'd you like to relieve Hank in the South Atlantic?" Tom asked Bud
upon their return.

Bud gave a whoop of excitement. "Roger!"

Tom slapped him on the back. "You can take off as soon as your ship's
provisioned. I'll join you later--but first," Tom added mysteriously, "I
have another job to attend to."

CHAPTER XVII

A MISSING AMULET

Bud's curiosity was instantly aroused. "Don't tell me you have a new
trick up your nautical sleeve to fox the Brungarians?"

Tom grinned. "That's the general idea. I hope to give hydrolung divers
the same protection that your jetmarine has."

"You mean make them invisible to sonar?"

"Yes," Tom replied, "and also give them personal spy gear to probe the
waters around them and spot an 'undetectable' enemy."

Bud whistled. "Do that, and I'll say you're _really_ a magician,
skipper!"

Tom himself transferred the analyzer from the _Sea Hound_ to Bud's
jetmarine. On a chance that it might become necessary to operate at
greater depths--either in searching for the lost missile or in shadowing
the enemy--Tom also assigned Arv Hanson the job of rigging the _Sea
Hound_ and another seacopter with his new inventions.

Four crewmen volunteered for the cruise. When the jetmarine was ready,
Tom and Bud exchanged tight handshakes.

"Good luck!"

"Thanks, Tom."

The young inventor waved as Bud disappeared down the hatch. As soon as
the craft had submerged, Tom went back to Shopton. That evening the
Swifts were enjoying a quiet dinner at home when a loud, growling buzz
shattered their mealtime conversation.

"Oh!" Sandy gasped. "The burglar alarm!"

The Swifts' house and grounds were protected by a secret magnetic field.
Any intruder breaking the barrier touched off the automatic alarm
system. To avoid the buzzing, the family and their close friends wore
wrist watches containing tiny neutralizer coils.

"I'll see who it is," Tom said, and hurried to the door, feeling a
twinge of apprehension.

_Was this a new attempt by Brungarian agents?_

He switched on the porch light and peered out cautiously through the
one-way glass pane in the door. A slim, hatless figure in a dark suit
was just coming up the steps. Tom gave a smile of relief.

It was Harlan Ames!

"Hi, Harlan!" Tom opened the door before Ames had a chance to ring the
doorbell. "We heard you coming!"

The security chief was startled when he realized he had activated the
alarm system.

"That's strange," he said uneasily. "Tom, I wonder if--"

He broke off to dart a quick glance at his wrist. Then his face relaxed
into a look of chagrin.

"Great! I forgot my wrist watch!" he murmured. "Haven't visited your
house in so long I neglected to wear it."

The other Swifts smiled in amused relief, and Mrs. Swift invited him to
join them for dessert. Ames, however, declined politely.

"Thank you, but I just finished dinner myself," he explained. "I dropped
by to--"

Once again Ames's voice trailed off in midsentence, as he reached into
the side pocket of his coat.

"My amulet!" he gasped. "It's gone!"

"Are you sure?" Tom said with quick concern.

Ames nodded as he frantically tried all his other pockets. The
electronic amulet to which he referred had been issued to all
Enterprises personnel and family visitors who used the private gate. The
amulets were contained in slender bracelets and were designed to trap
radar impulses. This prevented them from showing up as blips on the
giant detector radarscope mounted on the main building. The purpose of
the scope was to reveal unauthorized visitors or spies.

"My bracelet broke this afternoon," Ames said. "I slipped it into my
pocket to have it repaired. But it's not there now!"

Tom grabbed a flashlight and dashed outside for a hasty check of the
walk. Ames followed, to look inside his black sedan. But the amulet did
not come to light.

"Did you go home after you left the plant today?" Tom asked.

Ames shook his head worriedly. "No, I stopped at a restaurant. Mind if I
use your phone?"

"Go ahead."

The security chief called Enterprises and asked his assistant, Phil
Radnor, who was on night duty, to make a thorough search. While awaiting
the results, Ames also called the restaurant, but learned that no such
item had been turned in.

Half an hour later Radnor called back to report no luck. "The amulet may
show up yet, Harlan," he said. "But I'll alert the guards at the plant
to be on the lookout for an unauthorized visitor."

"Thanks, Phil." Ames hung up and turned away from the telephone with an
embarrassed look. "Fine example I'm setting as head of plant security,"
he murmured. "Let's hope the amulet wasn't stolen."

Excusing themselves from Mrs. Swift and Sandy, Tom Sr. and Jr. retired
with Ames to Mr. Swift's study to discuss the news he had brought.

"I had a late call from Admiral Walter this evening," Ames explained.
"The Navy's getting pretty desperate over that lost missile. They're
ready to co-operate with any moves you care to make. I take it you're
prepared to carry out a search on your own, Tom?"

The young inventor nodded. "Yes, as soon as I've perfected all the gear
I'll need--which won't be long, I hope."

Ames added, unhappily, that certain papers and news commentators had
been making snide remarks about the Swifts' failure to match the
Brungarians' submarine achievement.

"I think Tom has that situation pretty well in hand," Mr. Swift remarked
with a smile.

Tom gave Ames a full report on his own apparatus for rendering a
submarine invisible to underwater detection. Ames grinned at the news.
The grin grew even wider as he heard of the successful test of the
quality analyzer sonar.

"Bud Barclay's on his way to the South Atlantic right now with a fully
equipped jetmarine," Tom ended.

The next morning he eagerly tackled the job of adding sonar protection
and sonar detection features to his electronic hydrolung. What an
amazing fish man the wearer would be, Tom thought, if his project
succeeded!

It would enable a skin diver to operate indefinitely under water at
jet-propelled speed--invisible to enemy "eyes," yet be able to spy out
any hostile undersea prowlers, including supposedly "undetectable"
submarines!

Tom chuckled wryly as he mulled over the difficulties ahead. "Bud wasn't
kidding when he said it would take a magician!"

Besides his mask, electronic breathing device, density-control unit, and
ion drive, the wearer would now need at least three major
additions--first, sonar-blinding equipment with electronic control;
second, amplifying equipment to camouflage the wearer's noise under
water; and, third, a portable quality analyzer sonar.

"Whew! The miniaturizing job alone will be a king-sized headache!" Tom
said to himself. "I'd better start with a skin-diving suit made of that
molded plastic Arv is turning out."

After having some of the Tomasite sheathing, with its embedding
transducers, sent over from the plastics department, Tom cut out a suit
from a pattern and welded the seams electronically. He had just finished
wiring the control unit when Chow wheeled in a lunch cart.

"Got some _dee_licious steak-and-kidney pie today," the cook announced,
setting it out.

"Swell," Tom said absent-mindedly.

Chow frowned but left without interrupting the young inventor. Twenty
minutes later the cook poked his head into the laboratory again. Tom had
not yet touched his lunch.

"Brand my vitaminnies, start eatin', boss!"

"Sure, Chow."

By this time, however, Tom had become so absorbed in the task of
assembling some tiny monolithic blocks for the computer circuits of his
analyzer, that the lunch remained untasted. When Chow returned a third
time, Tom was startled by his bellow:

"Get your nose out o' that work, buckaroo, and _eat_!"

Realizing Tom's pie had cooled off, Chow had brought another serving,
hot from the oven. Seeing the stern look on the Texan's face, Tom burst
out laughing and obeyed meekly.

"I declare!" Chow chuckled. "One o' these days I'll have to force-feed
you if you won't pay no mind to your own nourishment!"

"Sorry, old-timer." Tom smiled. "Sometimes I do get a bit wrapped up, I
guess."

Hour after hour, Tom stayed glued to his workbench, sometimes busy with
delicate electronic gear, sometimes lost in thought as he pondered a
tricky problem in circuit design. It was long after dark when he drove
home from the experimental station, yet he was back on the job in his
laboratory early the next morning.

By lunchtime Tom had all the apparatus assembled. He was just trying on
the plastic suit, with all its accompanying paraphernalia, when Chow
made his usual appearance.

"Great sufferin' snakes!" the cook gasped. "You ain't goin' divin' in
_that_ getup, I hope! You look like a Christmas tree, boss!"

Tom nodded glumly. "Know something, Chow? That's just what I was
thinking myself."

The young inventor's suit was loaded down with the various electronic
units and festooned with wires. Even taking a few steps around the lab
convinced Tom that the design was too unwieldy.

"I'd probably either get tangled in seaweed or sink from sheer weight,"
he muttered.

Changing back to his slacks and T shirt, Tom began eating abstractedly
as Chow hovered around.

"If fishes could talk, I reckon you'd scare 'em half to death in that
rig!" Chow said, trying to cheer Tom.

"Fish do talk," the young inventor said. "At least they make noises.
Don't you remember that emergency fish-talk code we used when we were--"

Suddenly Tom paused, his mouth dropping open. "_Chow!_ You've just
solved my problem!" he exclaimed.

"I have?" Chow goggled at the young inventor.

"You sure have!" Tom bounced off his stool and began pacing about. "Now,
take porpoises. They utter all sorts of sounds--grunts, squeals,
jawclaps--and one particularly characteristic sound, like the grating of
a rusty hinge."

Chow scratched his chin uncertainly. "Wal, what about it?"

"Suppose I used that rusty-hinge noise to mask the diver's noise." Tom
turned and stabbed the air with his finger. "I could _also_ use that
same sound output as the search pulse for my quality analyzer sonar!"

In this way, Tom explained, he could eliminate part of his bulky
equipment and do an even better job of making the diver "invisible."

Bubbling with enthusiasm, Tom decided to buy a live porpoise at once and
make an exact recording of its sounds. As soon as he had finished lunch,
he put in a number of calls to suppliers of marine specimens. But none
could provide a porpoise on short notice.

"Guess I'll have to catch one myself!" Tom told Chow.

He drove out to the airfield and took off in a Whirling Duck for Fearing
Island. At the base, both Mel Flagler and Zimby Cox were eager to
accompany the young inventor when he told them about the trip he had in
mind.

Tom chose the _Sea Hound_ as the fastest and best suited craft for his
purpose. With Mel's and Zimby's help, he quickly rigged a plastic "tank"
in the stern cabin. Minutes later, the seacopter zoomed skyward, heading
for the Florida Keys.

The flight was a short one at transonic speed. Tom chose a sparkling
stretch of open water, a mile or so offshore from a palm-green islet.
Zimby agreed to stay aboard and tend ship while Tom and Mel went over
the side in hydrolungs.

The two glided about in the translucent blue depths, keeping in close
range of each other. The sea was alive with shimmering fish of every
hue, darting among the coral. Suddenly, as Tom veered around to rejoin
Mel, his eyes widened in horror.

A vicious-looking hammerhead shark was zeroing in, directly behind his
friend!

"Look out!" Tom yelled over his microphone.

CHAPTER XVIII

SMILEY THE SEA COW

Mel turned in the nick of time. The monster shark was bearing down on
him like an undersea express train. Overcoming a moment of panic, Mel
gunned his ion drive to dodge the attack.

As Tom watched in agonized suspense, he saw the shark's jaws open and
shut in a lightning snap at Mel's outstretched arm. Its razor-sharp
teeth missed their target by inches!

Mel's gasp of relief was audible over Tom's earphones. "Let's get out of
here!" he cried, arrowing away from the man-killer.

Suddenly Tom realized the full extent of their peril. A long, sweeping
coral reef, which extended above water, lay between them and the _Sea
Hound_. Unless they could round the reef in time, the shark had them
trapped!

"Quick! This way!" Tom exclaimed.

The shark was moving at blinding speed. As if sensing the boys' plan of
escape, it launched itself in a wide curving sweep to cut them off.

"We can't make it!" Tom gasped. "We'll have to fight!"

Both swimmers were armed with skin diver's knives as a precaution. The
two maneuvered to meet the killer's onslaught.

This time its broad nightmarish head was aiming straight at Tom. He
jetted off to the right, but the monster veered instantly. Its lashing
tail gave Mel a stunning blow.

As the shark's jaws gaped for a bite, Tom zoomed underneath the
man-eater and slashed its belly with his knife.

The shark, maddened, thrashed the water in a frenzy. Tom moved like
lightning to dodge a deadly blow from its bony tail. Again and again
they felt the horrifying brush of the killer's fins or armor-tough hide.
By this time, Mel had revived. Repeatedly the two boys dived to jab and
slash at the shark's soft underbelly.

Both were nearly exhausted when the monster at last went limp and
floated slowly up toward the surface. Pale with shock and fright, Tom
and Mel jetted back to the _Sea Hound_.

Zimby Cox was startled by their faces when they clambered aboard and
ripped off their masks. "What happened to you two?"

Tom told him. "Good night!" Zimby cried out.

After resting, Tom and Mel dived in again. This time luck was with
them. In less than twenty minutes they sighted a small porpoise.

"Think we can lure it back toward the _Sea Hound_?" Mel queried.

"We'll try," Tom replied.

The creature with the bottle-shaped snout was as friendly and playful as
most of its fellow dolphins. Too playful, Tom concluded, after vainly
trying to tease it into chasing them. Instead of following, it would
"tag" Tom or Mel quickly, then swim away, evidently expecting to be
chased in turn!

"I give up!" Mel snorted in disgust.

Tom grinned and bobbed to the surface. He waved his hand several times
in a prearranged signal. Zimby at last spotted him and brought the _Sea
Hound_ to the scene.

Raising his mask, Tom called, "Let's have the net!"

Zimby lowered a nylon net and some pieces of fish to the two swimmers as
they came alongside. With the food as bait they tried to lure the
porpoise to the seacopter. But just as they thought they had it, the
monster would scoot off.

"It's just laughing at us!" Mel fumed.

At last, after winning its confidence with several bits of fish, the
boys succeeded in snaring the porpoise. Tom clambered onto the _Sea
Hound_'s deck and helped Zimby haul their catch aboard. "Quacking"
reproachfully, it was lowered through the hatch and placed in the tank,
which was then pumped full of salt water.

As soon as the _Sea Hound_ arrived at Fearing, Tom phoned Chow Winkler
at Enterprises and asked him to fly out to the base.

"Pardner, how'd you like to ride herd on this critter and gentle it down
for me?" Tom asked, when he showed Chow the porpoise.

It had been transferred to a huge, glass-paneled tank which had been set
up just outside Tom's Fearing Island laboratory during his flight to the
Florida Keys.

"Reckon I kin try makin' friends with it," Chow declared.

The porpoise stared morosely at Chow. The kindly old Texan's heart was
touched by the odd creature. To his delight, it soon responded to his
friendly overtures and quickly recovered its good nature. By the next
morning the porpoise was playing catch with Chow, or else swimming over
to have its back scratched. The cook named it Smiley.

"She's kind of a sea cow," he told Tom, "and you got to talk to my
Smiley like any cow!" Tom grinned and refrained from explaining to Chow
that a real "sea cow" was a walrus.

Meanwhile, the young inventor was busy with his own experiments. By
means of a microphone placed in the tank, he made exact recordings of
Smiley's "talk." Using Mel Flagler as a subject, Tom also tape-recorded
the sound of a skin diver propelled through the water by ion drive.

The next step was to compare the sound pattern of the tapes. Tom
filtered out the difference in the two sounds with the correlation
calculator unit of one of his quality analyzer sonars.

"Uh-huh. So you got the difference betwixt Smiley's talk an' the noise
Mel made," muttered Chow as he watched the jagged lines of light
flashing on the pulse-check oscilloscope. "Now what're you fixin' to do
with it?"

"This will be fed into the diver's sonar along with his own noise
output," Tom said, "to make him sound like a porpoise."

Chow howled. "That I've got to hear!"

The young inventor worked feverishly throughout the day and into the
next, perfecting his new "porpoise sonar." Using microelectronic
components, he was able to reduce all the units to amazingly small size.

Next, Tom began tailoring himself a completely new skin-diving suit.
Mask, ion-drive jet, and the various hydrolung units were molded into
the plastic, with no loose wires or tubes showing.

Monday morning he was ready to try the outfit. The sonarscope with its
tiny viewing screen was strapped to his left forearm. Another small unit
was fastened to the inside of his wrist, with four plungers in
finger-tip reach.

"What in tarnation's that?" Chow asked.

"Simplified controls," Tom explained. "One's for breathing adjustment,
one's for the density unit, one is my ion-drive 'throttle,' and this
last is for the sonar pulse--which will duplicate the porpoise sound."

The suit worked perfectly in a tank test. Chow was amazed as he listened
to Tom gliding about, via an underwater microphone.

"If that don't beat all!" he declared. "Can't tell the difference 'twixt
you an' Smiley!"

As Tom emerged from the tank, the portly cook rolled up his own pantlegs
and waddled up the metal ladder to the tank brim. He summoned the
porpoise with a whistle and straddled its back.

"What in the name of aquanautics do you think _you're_ doing?" Tom
gasped.

"I'll show you a real broncobustin' act in the water," Chow bragged.

Smiley glided off gently at first, Chow fanning the air with his hat and
yipping like a rodeo star. He did, in fact, cling to his slippery perch
with considerable skill.

But suddenly Smiley began bobbing and humping like an eel. Chow's face
froze in alarm. A moment later the porpoise dived and the cook let out a
yell of terror, "He-e-elp!"

Roaring with laughter, Tom dived in and rescued him. "Guess he ain't
quite broke yet, pardner!"

"Reckon not."

Now that Tom had all his technical problems solved, he plunged eagerly
into the job of fitting out his expedition to the South Atlantic to
search for the lost Jupiter missile.

Besides the _Sea Hound_ and the other diving seacopter which had already
been rigged with antisonar and antidetection equipment, Tom ordered a
large cargo jetmarine to be similarly equipped.

Then he drew up a list of supplies and underwater search gear needed
for the missile hunt. Tom phoned orders to a dozen different
departments. Food, space-plant pills, extra clothing, tools, including a
midget atomic earth blaster, grappling hooks--nothing was overlooked.

"I'd better take along a Damonscope too," Tom reflected. "Judging by
those Navy reports, ordinary Geiger counters haven't revealed anything."

Tom's Damonscope, one of his early inventions, was a photographic device
which worked on fluorescent principles. It was amazingly sensitive to
any form of radioactivity--and the missile, of course, would be "hot"
from exposure to cosmic rays.

Meanwhile, Tom had ordered his new hydrolung suit, with its four-plunger
control unit and porpoise sonar, to be flown back to Enterprises. Arv
Hanson had promised to make up several duplicates with a team of
technicians working on all-night shifts.

Late the next afternoon Tom returned to the mainland to confer with his
father. Mr. Swift reviewed the expedition plans with approval.

"Suppose we call Admiral Walter now and set a time for the Navy to move
out of the missile area, so you can take over," his father said.

Tom agreed, and his father placed the long-distance call to Washington.
Moments later, Admiral Walter came on the line. Mr. Swift talked to him
briefly, then turned the phone over to Tom, who described his
preparations for the missile hunt. A time schedule of operations and
communications was quickly laid out.

The admiral was amazed to learn that Bud Barclay was already patrolling
the area. "Our ships haven't seen or heard him!" the officer exclaimed.
Suddenly Admiral Walter broke off. "Hold it, please, Tom! A code call is
just coming in!"

His voice was grave as he returned to the Swifts' line. "That message
was from your friend, Bud Barclay," Admiral Walter reported. "It looks
as if our enemy has found the missile!"

"Oh, no!" Tom groaned.

CHAPTER XIX

FLASH FROM THE DEPTHS

Tom was stunned by the news. "There's no chance of a mistake?"

"Judge for yourself," Admiral Walter replied. He read the message:

     HAVE JUST SIGHTED ENEMY CRAFT DREDGING OUT METAL OBJECT

Tom repeated the information to his father. Both Swifts were silent for
a moment, exchanging dejected looks. Then Mr. Swift remarked evenly:

"The game's never lost till it's over, son."

"You're right, Dad!" Tom exclaimed. Turning back to the telephone, he
said, "Admiral, I'm not quitting. We'll take off as soon as I can get
back to the base!"

With a hasty good-by to his father, and farewells to his mother, Sandy,
and Phyl by phone, Tom dashed out of the building. He sped to Arv
Hanson's workshop, and the new hydrolung suits were loaded onto a small
pickup truck and taken to the airfield. While flying back to Fearing
Island in a helijet, Tom received a radio flash from his father.

"Another message from Bud. He says the object dug up by the Brungarians
was _not_ the missile. It appeared to be the metal section of a ship's
prow, from some hulk buried in the silt!"

Tom was jubilant. "Terrific news, Dad! Our luck may be turning!"

At the rocket base Tom detailed crews for the three undersea craft which
were to take off on the expedition. Arv Hanson would captain one
seacopter, Mel Flagler the jetmarine, while Zimby Cox, Chow, and four
crewmen would accompany Tom in the _Sea Hound_.

Because of their sonar-blinding systems, Tom realized there was a chance
of the ships losing contact with one another--especially if their
analyzer sonars developed trouble. He therefore plotted their course to
the South Atlantic carefully, and issued orders for the antidetection
circuits to be switched off every half-hour for a position check.

"Report to your ships," he now ordered.

As Tom was about to leave base headquarters, Harlan Ames telephoned from
Shopton. "Bad news, Tom. Dimitri Mirov has broken jail!"

"Good night!" Tom stifled a groan of dismay. "How did it happen?"

Ames said the Brungarian had somehow fashioned a crude weapon and
overpowered the turnkey. Disguising himself in the guard's uniform, he
had slipped out before his victim was discovered.

"He must have had outside help within close call," Ames ended, "because
he seems to have made a clean getaway. The State Police have spread a
dragnet, but it doesn't look hopeful."

"He'll probably duck out of the country pronto," Tom surmised. "Anyhow,
this won't stop us, Harlan."

By nightfall the little fleet of three undersea craft was speeding
southward at periscope depth. Tom alternated at the controls with Zimby,
two hours on and two hours off. Sleep came in snatches, the crewmen
flopping on their bunks as the chance offered. Chow's tasty meals helped
break the monotony.

It was the following day when they reached the missile search area. Tom
surfaced the _Sea Hound_ and reversed blade pitch, then gunned the rotor
turbines for an aerial reconnaissance flight, while the jetmarine and the
other seacopter stood by in the water.

"Brand my guppies, it's some ocean, eh, boss?" Chow remarked in an awed
voice.

"Big enough, all right," Tom agreed with a grin. "And plenty of water to
search in."

"No sign of the Navy," Zimby said.

Tom nodded. "They pulled out on schedule."

"What about them Brungarian sidewinders?" put in Chow.

"That's the question!" Tom swooped down to rejoin the other two craft.
"We'll keep an eye out for enemy blips while we do our prospecting."

Rather than lose time trying to contact Bud, Tom decided to let him find
the _Sea Hound_. Accordingly, he switched off the antidetection system
and ordered all ships to submerge. Arv's seacopter and Mel's jetmarine
were to maintain close formation and stand guard while Tom's craft did
the actual searching.

Now the missile hunt began. Tom had plotted a concentric search pattern,
focused on the probable position worked out by the task-force computers.
After checking his fix on the automatic navigator, Tom switched on the
Damonscope and steered the _Sea Hound_ on a gradually circling course.

The Damonscope was mounted in a blister on the hull, its camera lens
pointing toward the ocean floor. The automatic developing film would
record any trace of fluorescence, and a red light would signal this
result to the pilot's cabin.

Minutes went by as the _Sea Hound_ nosed slowly along through the
gray-green gloom, its sister craft flanking it a hundred yards on either
side. They were moving only a fathom or so above the bottom.

"A blip at eleven o'clock!" the sonarman called out suddenly. Tom's
pulse quickened. "Moving straight toward us," the sonarman added.

Tom surrendered the controls to Zimby long enough to dart over and study
the sonarscope. "I've a hunch it's Bud," he told the others.

His guess proved correct when the unmistakable outline of a jetmarine
loomed into view. Tom flicked on the search beam for a moment, and Bud
could be seen waving through the cabin window. Then the yellow glare
went off, and Bud's jetmarine glided away to take up a scouting position
ahead of the _Sea Hound_.

An hour went by, then another. Suddenly a flash of light stabbed through
the murk from dead ahead.

"It's a signal from Bud!" Zimby exclaimed.

Tom nodded grimly. "He's spotted trouble--probably an enemy sub."
Silence settled over the cabin as Tom reached out to switch on the
antisonar circuits.

At that same instant a red light flashed on the control panel. "The
Damonscope!" Tom cried out. "We may be over the Jupiter prober!"

Cutting off the steering jets, Tom gave a brief flick on the reverse
jets to halt the craft. Then he turned over the controls to Zimby and
began stripping down to don a hydrolung suit.

"Gallopin' guppies! What're you aimin' to do?" Chow exploded.

"Go out and look for that missile," Tom said calmly. "It's what we came
for."

"Are you loco, boss? What about that sub Bud just spotted? Mebbe it's
Mirov's bunch!"

Tom refused to be dissuaded. After swallowing a space-plant pill, he
armed himself with an underwater flashlight.

"Think it's safe to show that light, skipper?" a crewman asked uneasily.

"If the enemy spots it, I'm hoping they'll think it's coming from a
school of lantern fish or sea anglers," Tom explained. He picked up a
three-pronged digging fork with his other hand and went out through the
air lock.

Tom glided back to the spot which the _Sea Hound_ had just passed over
and began digging into the silt. Presently he felt the fork strike
something hard.

"An obstruction!" Tom thought excitedly.

He probed deeper. Bit by bit, a smoothly contoured and still-shiny metal
surface became visible. "I've found it!" Tom's eyes flashed in triumph,
his heart pounding.

There was no doubt he had uncovered the nose cone of the missile which
had re-entered the earth's atmosphere tailfirst!

Meanwhile, Bud, keeping watch on the enemy submarine, had seen a shadowy
figure glide from its air lock and head in Tom's direction. Bud donned a
hydrolung and followed.

"What's that he's carrying?" Bud wondered.

Suddenly the answer came to him--a self-propelled underwater grenade!
Horrified, Bud jetted forward, tackling the diver at full speed.

A split second too late! The grenade went streaking straight toward Tom
Swift!

CHAPTER XX

A LUCKY BLAST

Tom's earphones caught the hiss of the approaching grenade. Instantly
his eyes darted to the sonarscope on his wrist.

A tiny blip of light was moving on the screen!

Tom whirled about, then gunned his ion drive. He pushed out of the path
of the grenade, which nevertheless grazed him as it streaked past.

Seconds later, the grenade struck bottom. A shattering _bo-o-oom_
reverberated through the depths, and clouds of silt darkened the water
into Stygian gloom.

Tom, knocked off balance, was tumbled about helplessly by the train of
shock waves. As they died away, he gradually recovered his bearings and
pressed the throttle control of his ion drive. It coughed and stuttered!
For a moment Tom felt a surge of panic, but the jet motor smoothed into
a steady purr of power.

"Whew!" he thought in relief. "At least I can still get around at full
speed if anything else comes at me!"

He had clung to the flashlight and fork despite the explosion. The blast
had hurled him away from the spot where the missile was buried, so Tom
began trying to locate it again.

But he soon realized that his efforts were hopeless. He must wait until
the silt which clouded the water cleared. Now Tom feared that the
explosion might have reburied the nose cone.

Suddenly a new worry gripped him. _Had the missile's precious contents
been destroyed by the blast?!_ Slowly he began making his way back to
the _Sea Hound_.

Unknown to Tom, Bud was fighting a desperate battle with his adversary
barely fifty yards away. The divers grappled each other in an
octopuslike duel. At such depths, their movements were impeded, as if by
oil.

The Brungarian pulled out the knife at his belt. Bud, a skilled wrestler
from high-school days, managed to twist his foe's knife arm behind his
back--then applied a punishing judo hold! The Brungarian gave an audible
screech of pain and dropped the knife.

"Now you're coming along with me!" Bud muttered. He gunned his jet,
forcing himself and his adversary toward the _Sea Hound_.

Moments later, they passed the seacopter's cabin window. Reaching the
air lock, Bud hammered for admission. The hatch opened quickly and his
prisoner was hauled inside. Bud followed.

Tom greeted him with a bear hug. "Hi, Bud, you old devilfish!" Turning
to the prisoner, Tom added "Who's this?"

"The rat who fired that grenade at you!"

The prisoner was wearing a frogman costume and a mask which hid the
lower part of his face. The man's dark eyes glittered in hate, as Tom
ordered him to remove his mask. Sullenly the prisoner obeyed.

Tom gasped. "_Dimitri Mirov!_" The name sent a shock through the
Americans aboard.

"Wal, I'll be jing-whistled!" Chow declared, then broke into a gleeful
cackle.

Under their scornful gaze, the Brungarian's own eyes wavered and his
shoulders slumped in an attitude of defeat. "What is the use?" he
muttered. "Again I have failed. My career is over now, just like my
brother's."

Tom seized the opening. "In that case, maybe you're ready to do some
talking now."

Mirov shrugged. "What do you wish to know?"

In answer to Tom's questions, Mirov admitted that his group, composed of
Brungarian rebel Navy men and rocket engineers, had sabotaged the
returning Jupiter probe missile, hoping to obtain its data for their own
use.

Their key agent in America was the man who had posed over the phone as
Lester Morris and masterminded the other attempts to kidnap Tom. He had
also taken the amulet bracelet from Ames's jacket in a restaurant.

Mirov himself had been given the bracelet after his jail break. Pulling
back the sleeve of his frogman suit, he displayed it with a momentary
smirk of pride.

"I even got inside the grounds of Swift Enterprises and stole a plane
that same night," Mirov boasted.

Tom was startled. "How did you manage that?"

"Very simple. I thumbed a ride with one of your trusted workers on the
late shift and showed him the amulet to identify myself as a Swift
employee. The guard at the gate was fooled the same way."

Tom nodded thoughtfully. "They were instructed to look for a man trying
to sneak past alone. Seeing you in the same car with a known employee,
he probably assumed you were all right."

Mirov was allowed to change into dry clothes, then his hands were bound
behind his back. When the water cleared, Tom and Bud ventured outside
again. First they headed for Bud's jetmarine to reassure his crew. Here
they learned that the mystery submarine had vanished.

"Good riddance!" Bud exclaimed jubilantly. "They probably didn't even
realize you had found the missile!"

"_Had found_ is right--past tense," Tom said wryly. "It's no doubt
buried again. But at least we have the right spot."

They emerged from the jetmarine and headed back toward the site. As they
glided astern of the _Sea Hound_, Tom uttered a cry over his suit mike.

"_Bud! There it is!_"

Both boys darted ahead at increased speed, and Tom played his flashlight
beam over the precious treasure. Instead of burying the missile deeper,
the grenade explosion had uncovered the entire nose cone and part of the
section behind it!

"Sizzlin' squids! What a break!" Bud whooped.

The boys jetted back to the _Sea Hound_ to announce the good news. Zimby
and two other crewmen were dispatched in hydrolungs to inform the other
ships. Tom requested them to remain submerged and guard the site.

Twenty minutes later the _Sea Hound_ was zooming up to the surface. Tom
hoisted the craft's aerial and radioed word to his father, who was
overjoyed. Mr. Swift, in turn, had news--that the rebels' key man and
Len Unger had been seized by the FBI. Tom's next call was to Admiral
Walter.

"Tom, this is wonderful news!" the admiral exclaimed. "I'll have our
Navy ships routed back there immediately--and I intend to fly out
myself as soon as I can board a plane!"

As Tom waited for the task force to arrive, his thoughts turned to new
inventions to tackle. But he could not anticipate what would happen to
him in his _Triphibian Atomicar_.

Within hours, the task force arrived at the site and recovery operations
got under way. The missile was hoisted to the surface by cables attached
to submarines, then hauled aboard the tender. Tom himself supervised the
job of extracting the sealed data section.

"You've done a tremendous job, Tom Swift, and our whole country will be
proud of you!" Admiral Walter declared before sailing home.

Tom grinned as he prepared to descend the ladder over the side. "Let me
know about life on Jupiter, sir. I may go there myself one of these
days!"