Holmes flicked the horse, and we drove away through the endless chain of empty streets, which widened gradually, until we were flying across a broad bridge, with the dark river flowing slowly beneath us. Beyond lay another dull deserted area, in the silence we could hear only the heavy, regular steps of the policeman. The dark clouds were drifting slowly across the sky, and a star or two twinkled here and there. Holmes drove in silence, with his head dropped upon his breast, and the look of a man who is lost in thought. I sat beside him, curious to learn what this new quest might be. It seemed to occupy his mind so sorely, but I was afraid to interrupt him. We had driven several miles, and were coming close to suburban villas, when he shook himself, shrugged his shoulders, and lit up his pipe looking like a man who has satisfied himself that he is acting for the best.