“I made up my mind that the fellow was in hiding in the house. When I paced one corridor and found it six feet shorter than the corresponding one below, it was pretty clear where he was. I thought he had not the nerve to lie quiet before an alarm of fire. We could, of course, have gone in and taken him, but it amused me to make him reveal himself. Besides, I owed you a little mystification, Lestrade, for your chaff in the morning.”

“Well, sir, you certainly got equal with me on that. But how in the world did you know that he was in the house at all?”

“The thumbmark, Lestrade. You said it was final; and so it was, in a very different sense. I knew it had not been there the day before. I pay a good deal of attention to matters of detail, as you may have observed, and I had examined the hall, and was sure that the wall was clear. Therefore, it had been put on during the night.”

“But how?”