"Well, Doctor, if that is the case, you can no doubt explain a few things that have been puzzling me. In the first place, will you tell me why, if you were not expecting another victim, you showed such surprise at the sight of the corpse? What reason could you have had for being so deeply interested in the relative positions of your roof--not your office, mind you, but your roof--and the room in which the body was found, unless you had noticed something unusual from that point of observation? Why were you so sure that the Derwent's flat was occupied, if you had not seen some person or persons there? By the way, I noticed that from your roof I could look directly into their windows. Again, you betrayed great surprise when Miss Derwent lifted her veil. Why did you do so, except that you had previously seen a very different looking person in her apartment? And why did you select the Atkins's two servants out of all the people in the building, to question about a certain noise, but that you yourself had heard a scream coming from their premises? And, lastly, you showed an unexplained interest in the back door of the Rosemere, which is particularly suggestive in view of the fact that this window is exactly opposite to it. I need only add that your presence on the roof during some part of Wednesday night, or early Thursday morning, is attested by the fact that I found some pipe-ash near the chimney. You smoke a pipe, I see" (pointing to a rack full of them); "your janitor does not, neither do your two fellow-lodgers. Besides that, all the other occupants of this house are willing to swear that they have not been on the roof recently, and those ashes could not have been long where I found them; the wind would have scattered them. You see, I know very little, but I know enough to be sure that you know more." I was perfectly dumbfounded, and gazed at the detective for some moments without speaking. "Well, granted that I was on the roof during a part of Wednesday night, what of it? And if I did hear or see anything suspicious, how can you prove it, and above all, how can you make me tell you of it?" "I can't," rejoined Mr. Merritt, cheerfully. "I can only ask you to do so." "And if I refuse?" "Then I shall have to delay satisfying my curiosity till we meet in court, but I do not doubt that my patience will then be adequately rewarded, for a skilful lawyer will surely be able to get at many details that would escape me, and I hardly think that you would resort to perjury to shield two women whom I am convinced you never laid eyes on before yesterday, and have certainly not seen since." The detective paused. I still hesitated, for I felt an extreme reluctance to further compromise that poor girl by anything I might say.