"Then what in heaven's name----?" I checked the exclamation on my lips. She was looking at me as her brother had done, but she seemed, at all events, to make up her mind more quickly. "Come with me," she said quietly. We walked to the building. There was a door at the side fitted with a Yale lock, but it stood slightly ajar. She pushed it open. The interior consisted of one single room, that seemed from its fittings half laboratory, half workshop. There were shelves around, containing bottles, chemical apparatus, a few books stacked together. A long table, littered with tubes and glasses, stood almost directly under the skylight. One corner of the room, to the right of the table, was screened off to form a dark-room, with the ordinary square of red glazed fabric let into the door. I looked around the place with curiosity. There was nothing here to account for the dog's behavior. The contents of the table at one end were confused and overthrown, and a strip of cocoa matting, which had evidently lain under or near the table, had been rolled and flung in one corner. The boards were noticeably cleaner where it had been lying, and near the edge of this clean space there was a stain, smudged as though purposely by someone's foot, but to my eyes an obvious blood-stain. Directly under the skylight, which was some four feet square, was the apparatus that for the moment puzzled me. It was mounted on a high stand that brought it near to the glass, and it looked like an acetylene lamp with very powerful concave reflectors; the kind of reflector, on a smaller scale, that is used in some lighthouses. The size of the lamp was quite outside the requirements of the room for ordinary lighting purposes, and the reflector seemed planned to throw the light outside the building, and in any desired direction. As I looked at it there flashed across my mind the recollection of the curious sort of searchlight I had seen the night before from my porch. Here was the solution of it, but I was puzzled to imagine what Lessing could be doing with an apparatus of this kind in such a place. I turned to Miss Lessing. "Was it here that your brother spent last evening?" "Yes. He came out here about nine o'clock, after dinner. He often works late, and we never sit up for him. My sister-in-law went to bed soon after; she had one of her bad headaches that she has been subject to for the last eighteen months. I sleep in the room next to hers, and I went to bed about eleven. I am an early riser, as a rule, and when I came out of my room this morning I met my brother just coming into the house." She paused, and I could see that she was struggling with the recollection. "He wouldn't let me touch him, and he only said something about wanting to sleep, and that I should send Doctor Lennox up to him. I left him in the sitting-room and went straight off." "Cycled?"