*

Even as he recognized her, Larry saw Von Ullrich lunge forward, seize
his captive and mount to the conning-tower with her--but before the
German could thrust her into the hatch, he had reached the U-boat's
side and clambered to her rescue.

Dropping Diane, Von Ullrich wheeled to face his assailant. They
grappled, fell to the deck, rolled over and over.

But suddenly, as they were struggling, there came a sound that caused
the German to burst free and leap to his feet.

It was the sound of engines under them!

Ignoring Larry now, Von Ullrich staggered to the conning-tower hatch.
It was battened fast. Frantically he beat on it.

This much Larry saw, as he knelt there getting his breath. Then he
rose, took Diane by the arm and led her down. And he was none too
soon, for with a lunge the U-boat got under way.

But she seemed unable to lift her loot-laden mass from the ocean
floor, and headed off crazily across the plateau, dragging her keel in
the sand.

With fascinated horror, they watched the craft's erratic course, as it
swung loggily westward and headed toward that yawning abysm from which
they had all so lately risen.

The last sight they had of the U-boat was as it reached the brink, its
despairing commander still standing in the conning-tower, hammering
vainly on that fast-bound hatch; then they turned away faint, as the
doomed craft plunged down, stern up, into those crushing depths.

* * * * *

Professor Stevens now joined them.

"A lesson in avarice," he said gravely, when he had greeted his
daughter with heartfelt relief. "And a typical fate of fortune
hunters! Let that be a lesson to you, young man."

"Amen!" said Larry.

"But what happened, my dear?" asked the professor of Diane, a moment
later. "Why were they in such a hurry to be off?"

"Because the sensible Antillians seized their opportunity and overcame
their guards, while we were below," was her reply. "When we got back,
we found the pyramids flooded, so there was nothing else for them to
do but go."

So that was the explanation of those gathering, furtive hosts in the
lower level, thought Larry. Now he knew what they had been waiting
for! They had been waiting for that usurping vandal to depart.

And how they must be gloating now, down there!

"But why were they so eager to abandon the _Nereid_?" asked the
savant, still puzzled. "It it a better boat than theirs, even if I do
say so myself."

"Be