"It will be a very interesting experiment," I said, looking as learned as I could. I thought I had kept my end up very well, and far from having to pretend to be interested, as Quarles had suggested, I was profoundly interested, not in the psychological discussion, but in the Bayswater mystery. I had heard of it before, and remembered that Martin, one of the oldest members of the force, had said that it was no more a case of suicide than he was a raw recruit. I am far from saying that no mystery is to be accounted for by the supernatural, but I always want to test it in every other way first. Quarles was pleased to jeer at me for a skeptic as we drove back to Chelsea. He did not consider me altogether a fool as a detective, but he had no use for me as a psychological student. "Anyway, it is a pity you are undertaking this business in your present nervous state," I said. "At least let me be with you on Friday night." "Nonsense, that would make the experiment useless. You clear up the mystery of this subtle scoundrel who has tried to get me shot and my nervous state will soon disappear." As a matter of fact, I couldn't settle to a careful study of my recent cases, as the professor had suggested. I tried and failed. I could not forget the experiment which was to be made on Friday night, and on Wednesday morning I took action. First of all, I arranged that a special constable should be on duty in Manleigh Road, and from his appearance no one would have supposed that anything in the way of a genius had been introduced into the neighborhood. He looked a fool; he was one of the smartest men I knew. Strangely enough, on the Thursday night No. 7 was burgled quite early in the evening as soon as it was dusk. Two men got in at a basement window, and the constable was quite close at the time. He had instructions, in fact, to give warning to the burglars if there was any danger of their being seen. I had not burgled the house alone; I had taken a young detective named Burroughs with me. Of course, I might say it was because I wanted to give him a chance, or because I thought we might encounter desperate characters in the house; but as a fact, it was the supernatural element which decided me. I do not like the idea of the supernatural; my nerves, excellent in their way and in their own sphere, are inclined to get jumpy under certain conditions. We went up from the basement cautiously, and it would have needed keen ears to have heard our movements. Without showing a light, we went into every room in the house. Those in front had some light in them from a street lamp outside, but those at the back were dark, although, after a while, we got accustomed to the dark, and could see to some extent. None of the blinds was drawn, and although there was no moon, it was a clear, starlit night.