“A simple case, and yet, in some ways, an instructive one,” Holmes remarked, as we travelled back to town. “It hinged from the outset upon the pince-nez. But for the fortunate chance of the dying man having seized these, I am not sure that we could ever have reached our solution. It was clear to me, from the strength of the glasses, that the wearer must have been very blind and helpless when deprived of them. When you asked me to believe that she walked along a narrow strip of grass without once making a false step, I remarked, as you may remember, that it was a noteworthy performance. In my mind I set it down as an impossible performance, save in the unlikely case that she had a second pair of glasses. I was forced, therefore, to consider seriously the hypothesis that she had remained within the house. On perceiving the similarity of the two corridors, it became clear that she might very easily have made such a mistake, and, in that case, it was evident that she must have entered the professor’s room. I was keenly on the alert, therefore, for whatever would bear out this supposition, and I examined the room narrowly for anything in the shape of a hiding-place. The carpet seemed continuous and firmly nailed, so I dismissed the idea of a trapdoor. There might well be a recess behind the books.