"And opened them with a purpose," I reminded him.
He said nothing in reply. Having secured the doors, he motioned to me to go in front, which I did, carrying the light, and in that order we came to my room. I would have handed him the lamp at the door, but he motioned to me to go in, and, following himself, closed the door. I set down the lamp, and waited for what he had to say. He was a long time coming to it; he wandered about the room for a time, stopping now and then, with his back to me, and with his finger tracing out the pattern of the wall paper. When at last he spoke he was still tracing that pattern, and he did not look round.
"You have done me a service to-night, and one I'm not likely to forget," he said.
"A service?" I asked in amazement. "I should scarcely have thought you'd call it that."
"I do—I do!" he exclaimed, swinging round upon me suddenly. "I meant to kill her, and you've saved me from that. I thank my God for it!"
"I don't believe you," I said doggedly. "You planned the thing too well for that."
"I did not plan it, except by the opening of the doors," he said. "I knew that she walked in her sleep sometimes, and I thought——"
"You lie!" I exclaimed fiercely. "I watched you, and heard you while you suggested to her that she should walk in this eastern corridor at midnight, and should come to the end wall. And you knew that there would be no wall there."
He looked at me in a bewildered fashion for what seemed a long time; then he nodded slowly twice. "So you heard that, did you? Well, I suppose there's nothing for it but confession. I did plan the thing; it was by a method you don't understand—what we call hypnotic suggestion. That means that you tell a person that they are to do a certain thing at a certain hour, and when that hour arrives they must inevitably set about to do it."
"Why did you want to kill her?"