“I went back into the laboratory and hunted over every square inch of it, but I found nothing. I stood there puzzling. If there had been some power that had killed Heidenmuller, there must have been some material substance in which it was kept. I had made the most careful inquiries about the things on his person and in the room. No one could tell me anything. Swenton and Griegen, the two assistants, were neither of them there, but the first one who had entered the room when the doctor’s body was found was a sharp-faced lad who acted as janitor. I had questioned him thoroughly, as I thought, but I resolved to see if he did not know more. I went to him again, and a lucky inspiration came to me. Holding a sovereign in my hand I remarked casually, ‘If there is any little personal memento of the doctor left, I should like very much to have it.’ The narrow eyes of the lad gleamed. He thrust his hand into his pocket, and drew out what was apparently a leather cigarette case, snatched the sovereign, and handed me the case. ‘Found h’it h’on the floor, h’after we took ’im h’out,’ he mumbled. ‘H’it’s the h’only think was there.’” Hamerly rose as he spoke and walked to his desk. I followed, my heart pulsating with great leaps. He took from a drawer what seemed to be a pigskin cigarette case, cut in half. Hamerly held the two sections out on his hand. At the top was a queerly constructed valve,--the case was lined with a black substance that looked like rubber. “I believe,” said Hamerly gravely, “that in this case there was some terrifically powerful substance, which killed Heidenmuller and destroyed all the metal in the wooden room, by escaping through the accidentally opened valve. I believe the man who is trying to stop all war uses the same dread agent. I believe, once the substance escapes and does its work, that it turns to a harmless gas, as hydrogen, once it has been exploded with oxygen, forms harmless water, or as the carbon of coal, which has blazed when united with the oxygen of the air becomes, after that union, inert carbon dioxide. You know, now, all I know. I’ve done all I could with it,” he ended, “Take it to Haldane.” Dazed with the story, I could only thank him and take the case. We parted with a word of good will, and assurance of secrecy on his side. CHAPTER XII I threw up my curtain next morning to find London settling down into a sea of fog. Already the Thames was wholly hidden, and the water side of the embankment showed only faint, twinkling lights, just on the point of complete extinguishment. The caped policeman, the hurrying butcher’s boy, the laborers and the charwomen passing through the garden below, had all completely lost their individuality and became, in place of common London types, misty twentieth century Niobes. But dismal though it was without, my spirits were cheerful enough within as I started down to meet Tom and Dorothy.