And all the time, Larry had an uneasy feeling of gathering furtive hosts about them, waiting--waiting for what? He confided his fears to no one, though he noted with relief that Von Ullrich seemed to sense these unseen presences too, for he proceeded with caution and always kept a strong guard outside. * * * * * By early afternoon, the _Nereid_ was one great coffer-chest. But still the rapacious U-boat commander was unsatisfied, though Professor Stevens began to have doubts if his craft could lift that massive weight of plunder to the top of the plateau. "One more load and we go," he soothed. "A few more pretties for the little lady!" Larry writhed, and should have suspected then and there--but as it was, the blow fell unexpected, stunning. Filing from the lock, they failed to notice that Von Ullrich and his crew hung back, until there came a sudden, guttural command, whereupon Diane was seized and the massive door flung shut in their faces. Appalled by this overwhelming disaster, the party stood for a moment motionless, speechless. Then, as one, Larry and the professor rushed forward and beat upon that barred hatch, calling upon Von Ullrich to open it. From within the submarine, through their vibrators, they heard him laugh. "_Auf Wiedersehen!_" he toasted them. "I now have all the treasure I want! The rest I leave to you! Help yourselves!" Even as he spoke, the _Nereid's_ auxiliary propellers started churning the water. Slowly, sluggishly, like some great gorged fish, the sturdy craft moved off, lifted her snout, headed upward. * * * * * Professor Stevens bowed his head, and Larry could well picture the grief that distorted the graybeard's face, inside that owl-eyed helmet. "Cheer up!" he said, though his own face was twisted with anguish. "Perhaps--" Then he paused--for how could he say that perhaps the situation wasn't as bad as it seemed, when it was obviously hopeless? "My poor Diane!" moaned the professor. "Poor child. Poor child!" As for Captain Petersen and the crew, they said nothing. Perhaps they were thinking of Diane, perhaps of themselves. At least, they knew it was over. Or so they thought. But to Larry, suddenly, occurred a gleam of hope. That strange sense of unseen presences! It was bizarre, of course, but doesn't a drowning person catch at straws? And Lord knows they were drowning, if ever anyone was! He turned and confided to Professor Stevens his idea, which was to retrace their steps within the city gates, seek out the populace and throw themselves on their mercy. The stricken savant, too, grasped at the straw. "It seems fantastic, but after all it is a chance," he admitted. So they pushed back into that great submerged city, with Captain Petersen and his skeptical crew. They entered one of the largest of the temples, wandered forlornly through its flooded halls and corridors, seeking some sign of these alleged beings Larry had sensed.