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!"