“I must explain here how I came in possession of this trump card of mine. It was through two casual observations, which at first never struck me as bearing in any way upon the matter I was investigating. The first was the annoying, almost impossible tidiness of Digby-Coates’s hair. It did not appear to be greased or pomaded in any way, and yet I never saw it other than as if he had just brushed it, and with care. The second was his curious trick of sitting on the edge of a chair with his feet thrust first backwards through the gateway formed by the front legs and then outwards until each instep is pressed against the back of each of those front legs. It is a trick most boys have, but it is unusual to find it persisting in a man of middle-age. Digby-Coates does not, of course, always sit like that, but frequently.
“What changed these two chance observations—the sort of thing one idly notices about any man of one’s acquaintance without really thinking about them—into perhaps the most important minor step in my case was a glimpse I had of Digby-Coates from the very point from which the servants who made his alibi had seen him. He was sitting as they had seen him sit (though I did not know this until I questioned them) in the big arm-chair, which was facing the window. All I could see from the passage was the long, solid back of the chair, the top of the well-tended head, six inches of each trouser-leg, and the soles of two shoes. On the open door was a notice: ‘Busy—Please do not disturb.’
“The scene was, in fact, a replica of what I had gathered it to be on the night of the murder. I fell to thinking, and suddenly the most annoying pieces of my jig-saw puzzle fell into place. I went in and spoke to him. I looked, more carefully than ever before, at his head, and came to the conclusion that he was bald, but wore the most skilfully made toupé I had ever seen. I remembered that he had told me that he never used a valet. I pictured him—he is the type—as one to whom the thought that any one else knew how unsavoury he appeared minus hair was abhorrent.
“When I discovered the toupé, I knew that I could smash the alibi if only the unknowing alibi-makers gave me, honestly, the answers I wanted.
“As you know, they did. I consider the matter clear, but I know it. Perhaps I had better show what Digby-Coates did that night; how he set his stage and played out his one-act show.
“He retires to his room, knowing that Hoode is in his study, Deacon busy or, as often of late, out, Miss Hoode and Mrs. Mainwaring in their beds, and some of the servants, as he wishes them, moving about the house—he has studied their movements and knows that on this night of the week there is work to do which keeps them later than usual. Luckily for him, the night is hot. It gives the necessary excuse for leaving his door as well as his window open. Upon that open door—which is not back against the wall, but only half open—he places a notice: ‘Busy—Please do not disturb.’
“(Observe the cunning of this notice. He had, I found from the servants, placed such a notice on the open door on two previous occasions. This, I am sure, he had done for a two-fold reason: (i) to see whether it would really keep out intruders, and (ii) to ensure, when eventually he placed it there on the night he chose for the killing of Hoode, that though the household were not become sufficiently accustomed to it to avoid a glance at it and subsequently into the room, the sight of the notice was yet familiar enough to ensure that it was not remarkable as being without precedent. He had, you see, for the sake of his alibi, to make certain that people passing (i) would look into his room; (ii) would not come in; and (iii) would not think the notice anything out of the ordinary.)
“Having placed his notice he draws his arm-chair up to its familiar position facing the window. Then he has to wait. Sometimes he sits. Sometimes, the waiting too hard upon even such nerves as his, he paces the room.
“All goes well. Every one, everything, plays into his hands. The very man he has chosen to incriminate draws the noose, by that request for the time, tighter round his own neck. The leaden-footed minutes, what with this incident, that of Belford, and the increasing certainty of success, begin to pass more swiftly. People go their ways past his door but do not enter.
“At last it is time. He gets his knotted rope, secures it to the leg of the carpenter’s bench Hoode has had fitted for him. The bench is clamped to the floor; no doubt but that it can stand the strain.