He paused for a moment, and then continued, a sinister purpose in his voice: “And now the end has come. It is not the end I sought, but I welcome it as well as any other. We two will pass out of this world together, Dr. Priestley, you the last victim of my justice, and I the executioner. It is but anticipating my own death for a short time, and the means I shall employ will render even deeper the mystery which surrounds me. On Sunday morning the world will hear of two more strange deaths in Praed Street. I think your secretary will come round here before the night is over, and, being able to obtain no reply, will call in the police to his aid. How much of the riddle will they solve, I wonder?” The Black Sailor stretched out his hand, and switched on a small electric hand-lamp which stood on a table by his side. “That will give us sufficient light for our purpose,” he said sombrely. Then, before the Professor could guess his intention, he suddenly leapt from his chair, turned out the gas which was burning at a bracket by the mantelpiece, and with a powerful wrench tore the bracket itself from the wall. It fell with a crash into the fire-place. Then the Professor understood. He, too, leapt from his chair with a shout, and dashed blindly for the door. But the Black Sailor was there before him. “It is useless, Dr. Priestley,” he said menacingly. “The door is fastened securely, as is the window. The chimney is blocked, and there is no possible escape for us. I doubt if you would be heard if you call again for help, but I cannot risk it. Will you give me your word to wait quietly, or must I gag you and tie you up? Would you care to meet death bound like a criminal, Dr. Priestley?” For a moment the two men stood face to face, the powerful form of the Black Sailor towering threateningly over the Professor. Behind them, with a faint hissing sound, the gas poured into the room through the broken bracket. Already the pungent smell of it caught Dr. Priestley by the throat. And then, suddenly, the idea came to him. It was a forlorn, desperate hope, a scheme almost as dangerous as waiting supinely for the fatal vapours to overpower him. Yet—it was worth trying. He nodded his head almost briskly. “I will not call for help,” he said, and, turning on his heel, he sat down again in the chair he had just quitted. The Black Sailor followed his example, and so the two sat in silence, waiting, waiting. The atmosphere of the room grew thick and heavy, difficult to breathe. The Professor found his thoughts floating away to trifling things, he imagined himself a boy again, at school— With a mighty effort of will he recalled them, forcing his mind to concentrate upon the thing he had to do. Yet, was it worth it? Death, in that comfortable chair, would be so easy. A pleasant languor crept over him. He had only to close his eyes and sleep——