's here," Bud murmured.

"Don't bank on that," Tom said. "They wouldn't be apt to advertise their
presence to passing ships or planes."

Tom nosed inshore as closely as he dared from sonar soundings, finally
easing the _Sea Hound_ up to a rocky reef that fingered out from the
beach. Then he, Bud, Hank, and Arv clambered out, armed with wrecking
tools and powerful flashlights.

Chow, in spite of his muttered grumblings, was ordered to stay aboard
and guard the ship with the other two crewmen who had come along.

Tom led his party cautiously ashore from the reef. They probed the
darkness of the beach. Their footfalls sounded eerily in the night
silence, broken only by the soughing of the sea wind and splash of
breakers.

"Good place for spooks!" Bud whispered jokingly.

A steep draw led upward among the rocky slopes. A hundred feet on, Tom's
group found the black yawning mouth of a cave. The yellow beams of their
flashlights revealed a tunnel leading downward inside. Tom checked with
a pocket detector. Its gauge needle showed no field force caused by
electrical equipment in operation.

"Okay, let's go in!" Tom murmured.

Cautiously they moved into the tunnel. Then suddenly ahead of them a
powerful dazzling light burst on, nearly blinding the searchers!

CHAPTER XIX

A FIENDISH MACHINE

A chill of fear gripped Tom and his companions as they blinked
helplessly in the glare! Had the enemy detected them the first moment
they had set foot on Balala Island? Had they walked blindly into a trap?

Gradually Tom's eyes and those of his friends adjusted to the dazzling
radiance. A door, blocking the tunnel just ahead, had slid open and the
light was pouring out of a room beyond.

"What happened?" Arv gasped.

Tom pointed downward to a pedallike plunger inserted in the tunnel
floor. "This must be a switch," he explained. "When I stepped on it
accidentally, it must have opened the door and flashed on the lights."

Bud whistled. "Wow! Let's be thankful it wasn't a booby trap!"

"Maybe it is," murmured Hank grimly.

Steeling their nerves, and with every sense alert, the searchers
advanced into the secret room.

Tom suddenly gave a cry of amazement. "The earthquake machine!"

A huge hydraulic device, with massive steel bed and supporting pillars,
looking somewhat like the enormous body presses found in automobile
plants, stood embedded in a recess in one wall.

Tom rushed to the machine and examined it in