“It is singular, certainly,” said Dr. Egerton, “though I don’t know that it helps us much.  Shall we withdraw the dagger before moving the body?”

“Certainly,” replied Thorndyke, “or the movement may produce fresh injuries.  But wait.”  He took a piece of string from his pocket, and, having drawn the dagger out a couple of inches, stretched the string in a line parallel to the flat of the blade.  Then, giving me the ends to hold, he drew the weapon out completely.  As the blade emerged, the twist in the clothing disappeared.  “Observe,” said he, “that the string gives the direction of the wound, and that the cut in the clothing no longer coincides with it.  There is quite a considerable angle, which is the measure of the rotation of the blade.”

“Yes, it is odd,” said Dr. Egerton, “though, as I said, I doubt that it helps us.”

“At present,” Thorndyke rejoined dryly, “we are noting the facts.”

“Quite so,” agreed the other, reddening slightly; “and perhaps we had better move the body to the bedroom, and make a preliminary inspection of the wound.”

We carried the corpse into the bedroom, and, having examined the wound without eliciting anything new, covered the remains with a sheet, and returned to the sitting-room.

“Well, gentlemen,” said the inspector, “you have examined the body and the wound, and you have measured the floor and the furniture, and taken photographs, and made a plan, but we don’t seem much more forward.  Here’s a man murdered in his rooms.  There is only one entrance to the flat, and that was bolted on the inside at the time of the murder.  The windows are some forty feet from the ground; there is no rain-pipe near any of them; they are set flush in the wall, and there isn’t a foothold for a fly on any part of that wall.  The grates are modern, and there isn’t room for a good-sized cat to crawl up any of the chimneys.  Now, the question is, How did the murderer get in, and how did he get out again?”

“Still,” said Mr. Marchmont, “the fact is that he did get in, and that he is not here now; and therefore he must have got out; and therefore it must have been possible for him to get out.  And, further, it must be possible to discover how he got out.”

The inspector smiled sourly, but made no reply.

“The circumstances,” said Thorndyke, “appear to have been these:  The deceased seems to have been alone; there is no trace of a second occupant of the room, and only one half-emptied tumbler on the table.  He was sitting reading when apparently he noticed that the clock had stopped—­at ten minutes to twelve; he laid his book, face downwards, on the table, and rose to wind the clock, and as he was winding it he met his death.”

“By a stab dealt by a left-handed man, who crept up behind him on tiptoe,” added the inspector.

Thorndyke nodded.  “That would seem to be so,” he said.  “But now let us call in the porter, and hear what he has to tell us.”