Talbot laughed incredulously. The walls of the room were smooth, and hard to the touch. "They're as solid as concrete," he said. "But cut like cheese under a steel blade. I found that out. Watch." To Talbot's amazement the point of the penknife sank into the wall and in a moment a section of it was gouged out. The professor said tensely, "I've been months in this place, been taken back and forth, and know the lay of the land. This room is in a great building that houses the laboratory from which the attack against earth is being launched. Would you believe it, only the great scientist who picked up my messages and helped me perfect my invention, and a few of his assistants, are concerned in that attack, and they will be congregated at the machines. Follow me, and whatever I command, do it promptly." The Professor had been working feverishly as he spoke, and now he and Talbot crawled through the hole he had made in the wall and found themselves in a long gloomy corridor. "Quick," Reubens whispered. They darted down the passageway. Talbot had only time to see that the gleaming sides of the corridor were beveled and etched with strange designs, before they came to its end and where a curious device like a huge five-pointed star was revolving noiselessly, half sunk in a great hole in the floor. Without hesitation the Professor stepped onto one of the flat-tipped star-points as it came level with where they stood and Talbot did the same. Up, turned the star-point, to a dizzy height, and over, but the tip swung on ball-bearings, maintaining its passengers in a perpendicular position, and from its highest point of elevation descended to another floor far below, where they disembarked. The huge revolving star-wheel was nothing but an ingenious movable staircase. But the Professor gave Talbot no time to marvel, nor did the latter try to linger. The corridor below was wider, more richly beveled and carved, and the statue of an heroic bird stood perched in the center of it. The lighting was soft and mellow, but Talbot could perceive no windows or globes. Suddenly from an open doorway hopped a bird. There was no chance to avoid it. Its wings were spread and from its parted bill came a harsh cry, "Toc-toc, toc-toc!"