I had not to cast about very long for the motive a man might have in forcing his feet into Manderson's narrow shoes. The examination of footmarks is very well understood by the police. But not only was the man concerned to leave no footmarks of his own. He was concerned to leave Manderson's, if any; his whole plan, if my guess was right, must have been directed to producing the belief that Manderson was in the place that night. Moreover, his plan did not turn upon leaving footmarks. He meant to leave the shoes themselves, and he did so. The maidservant had found them outside the bedroom door, as Manderson always left his shoes, and had polished them, replacing them on the shoe-shelves later in the morning, after the body had been found. When I came to consider in this new light the leaving of the false teeth, an explanation of what had seemed the maddest part of the affair broke upon me at once. A dental plate is not inseparable from its owner. If my guess was right, the unknown had brought the denture to the house with him, and left it in the bedroom, with the same object as he had in leaving the shoes; to make it impossible that any one should doubt that Manderson had been in the house and had gone to bed there. This, of course, led me to the inference that _Manderson was dead before the false Manderson came to the house_; and other things confirmed this. For instance, the clothing, to which I now turned in my review of the position: if my guess was right, the unknown in Manderson's shoes had certainly had possession of Manderson's trousers, waistcoat and shooting jacket. They were there before my eyes in the bedroom; and Martin had seen the jacket--which nobody could have mistaken--upon the man who sat at the telephone in the library. It was now quite plain (if my guess was right) that this unmistakable garment was a cardinal feature of the unknown's plan. He knew that Martin would take him for Manderson at the first glance. And there my thinking was interrupted by the realization of a thing that had escaped me before. So strong had been the influence of the unquestioned assumption that it was Manderson who was present that night, that neither I nor, so far as I know, any one else had noted the point. _Martin had not seen the man's face; nor had Mrs. Manderson._