The significance of the curious butt found by the electrician in the lamp-holder was not so clear. It seemed reasonable to assume that nobody but the dead man had entered the premises after they had been locked by the foreman on Saturday morning. Whyland had examined all the doors and windows very carefully, and had satisfied himself that they bore no signs of violence. He could account for both keys, and although it was possible that a third key existed, it seemed unlikely that anyone had used it between 12:30 and two. Again, since the door had been found bolted on Monday morning, it was probable that the dead man had bolted it behind him, and that he was alone in the house when he died. The foreman had assured him that he had found the windows fastened inside, and that it was only by the use of a special tool that he had been enabled to open the one at the back. It looked very much as if Martin had himself fixed the butt in the lamp-holder. But why?