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 ey