"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.

[Ill.u.s.tration]

"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 s.p.a.ce-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-p.r.o.nged 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 pa.s.sed 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 pa.s.sed 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!"