He was soon to know, for now the gallery they had been traversing levelled out into a series of short pa.s.sages, each barred by a heavy stone door, and finally they were led into a small, square room, barely large enough to admit them all.

There, with gestures toward the far end, their guides left them.

The door closed, and almost immediately another on the opposite side opened, slowly at first, then wider and wider, admitting a rush of water that promptly filled the room.

Stepping wonderingly out, they found themselves on the upper level, beside the second of the two smaller pyramids.

"Whew!" gasped Larry, as they stood looking around, still a little dazed. "These people are sure quick-change artists! First they try to feed you to their G.o.ds, then they save you from almost as bad a fate.

Dizzy, I call it!"

"Quite understandable, I should say," declared the professor. "Unable to cope with Von Ullrich themselves, they think perhaps we may be able to."

"Well, let's hope they're right!" grimly. "If once I get my hands on him--"

He broke off suddenly, as Captain Petersen called out:

"The _Nereid_! There she is!"

Following with their eyes the bright segment cut into the murky depths by his flashlight, they saw the familiar outlines of their craft; and close beside her lay the U-boat.

A feverish activity seemed to be going on between the two submarines.

"They're changing cargo!" cried Larry. "Quick! We've got them now!"

But the progress they were able to make, hampered by their heavy suits, was maddeningly slow. Their searchlights, moreover, betrayed their approach. Before they could reach the scene, most of the sailors had abandoned their task and piled into the U-boat.

Arms swinging wildly, Von Ullrich stood beside it, trying to rally then. Refusing to risk combat, however, since they were unable to use their deadly hand-grenades under water, they continued clambering up the sides of their submersible and shoving down through its conning-tower hatch.

Now a figure in a familiar pressure-suit broke away and started toward the advancing party.

It was Diane!

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 a.s.sailant. 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 ma.s.s 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."

"Because I put it out of commission, directly we got back up here,"

replied Diane. "But not permanently!" she added, with what Larry knew was a smile, though he couldn't see her face, of course, through the helmet of her pressure-suit.

"Little thoroughbred!" he exclaimed, half to himself.

"What did you say, Mr. Hunter?--Larry, I mean," she inquired.

"N--nothing," he replied uneasily.

"Fibber!" said Diane. "I heard you the first time!"

"Just wait till I get out of this darned suit!" said Larry.

"I guess I can wait that long!" she told him.

And if Professor Stevens heard any of this, it went in one ear and out the other, for he was thinking what a report he would have to make to his confreres when they got home--particularly with half a boatload of a.s.sorted idols for proof.

[Ill.u.s.tration: He pressed the tiny switch in the flame-tool's handle just as Arlok came through the door.]

The Gate to Xoran

_By Hal K. Wells_