tily from the galley. "Pore lil ole boys," he
fussed. "Brand my snorkel, I never should've let you young'uns go pokin'
around down below there without me around to keep an eye on things!"

Tom slapped the loyal old Texan on the back. "If you want a dive, come
along."

"You're goin' back down?" Chow asked.

"In the seacopter," Tom replied. "To find out, if possible, who fired
that projectile at us."

"Then count me in!" Chow declared, stripping off his apron. "I just hope
I get my hands on them sneakin' polecats!"

Slim Davis would pilot the _Sky Queen_ back to Shopton at once, because
of Bud. Tom and Chow, meanwhile, would join Hank and his crew aboard the
_Sea Hound_.

Ten minutes later the sleek seacopter, its searchlight off to avoid
detection, was plummeting downward through water that changed before
their eyes from greenish blue to a deep-gray gloom. Iridescent fish
darted past the cabin window.

"Think the enemy sub was searching for our Jupiter prober?" Hank asked.

"It must have been," Tom reasoned.

Hank frowned. "Which means they must have figured out the missile's
position as fast as our side did."

"And they'll play rough to stop us from finding it," Arv added
forebodingly.

Within moments, the group clustered in the pilot's cabin felt a gentle
bump as the _Sea Hound_ settled on the submerged plateau. Tom relaxed at
the controls but kept the rotors going so the craft would remain
submerged. Meanwhile, the sonarman was probing the surrounding waters.

"Any pings?" Tom asked.

The man shook his head without taking his eyes from the sonarscope.
"Nothing yet."

Hank Sterling donned a hydrophone headset and listened intently. The
silence deepened in the _Sea Hound_'s cabin. Suddenly Hank stiffened and
the sonarman cried out:

"A blip, skipper! At two o'clock!"

It was moving rapidly on the scope--something streaking toward their
starboard beam!

"Good night! It's another missile!" Tom gasped.

He darted back to the controls and gunned the reverse jets just in time!
The missile flashed across their bow.

"Great bellowin' longhorns!" Chow gasped weakly. His leathery face had
gone pale under its tan. "The yellow-livered drygulchers!"

"I don't get it," Arv Hanson spoke up. "If they're in firing range, we
should have detected them, shouldn't we?"

Tom nodded grimly. "Whoever our enemies are, they must have perfected a
way to make themselves invisible to underwater detection.

"_And we'll