David Guinness strained at the rope. It was futile, but in doing so he twisted his head around and saw another form, similarly tied, lying close to him. He gave a little cry of relief. It was Sue. And she was conscious, her eyes on his face. She spoke to him, but he could not understand her for the drone in his ears, and when he spoke to her it was the same. But the professor did not just then continue his effort to converse with her. His attention was drawn to the borer, now dimly illuminated by its portable light, which had been secured to the door. It was right side up, and appeared to be undamaged. The broad ray of the searchlight fell far away on one of the cavern's rough walls. He could just make out James Quade standing there, his back towards them. He was hacking at the wall with a pick. Presently he dropped the tool and wrenched at the rock with bare hands. A large chunk came loose. He hugged it to him and turned and strode back towards the two on the floor, and as he drew near they could plainly see a gleam of triumph in his eyes. "You know what this is?" he shouted. Guinness could only faintly hear him. "Wealth! Millions! Of course we always knew the radium was here, but this is the proof. And now we've a way of getting it out--thanks to your borer! All the credit is yours, Professor Guinness! You shall have the credit, and I'll have the money." Guinness tugged furiously at his bonds again. "You--you--" he gasped. "How dare you tie us this way! Release us at once! What do you mean by it?" * * * * * Quade smiled unpleasantly. "You're very stupid, Guinness. Haven't you guessed by now what I'm going to do?" He paused, as if waiting for an answer, and the smile on his face gave way to a look of savage menace. For the first time his bitter feelings came to the surface. "Have you forgotten how close I came to going to jail over those charges of yours a year ago?" he said. "Have you forgotten the disgrace to me that followed?--the stigma that forced me to disappear for months? You fool, do you think I've forgotten?--or that I'd let you--" "Quade," interrupted the older man, "you know very well you were guilty. I caught you red-handed. You didn't fool anyone--except the jury that let you go. So save your breath, and, if you've the sense you were born with, release my daughter and me. Why, you're crazy!" he cried with mounting anger. "You can't get away with this! I'll have you in jail within forty-eight hours, once I get back to the surface!" With an effort Quade controlled his feelings and assumed his oily, sarcastic manner. "That's just it," he said: "'once you get back!' How stupid you are! You don't seem to realize that you're not going back to the surface. You and your daughter." Sue gasped, and her father's eyes went wide. There was a tense silence. "You wouldn't dare!" the inventor cried finally. "You wouldn't dare!"