"On this enlargement of the wound," continued Malcolm Sage, "you will see an abrasion on the side nearer the ear, as if the head had suddenly been jerked backwards between the time of the muzzle being placed against the temple and the actual firing of the shot." Thompson leaned across to examine the photograph. "If the eyes of someone sitting at a table are suddenly and unexpectedly covered from behind, the natural instinct is to jerk backwards so that the head may be turned to see who it is. That is exactly what occurred with Challoner. He jerked backwards, and the barrel of the pistol grazed the skin and was deflected still more towards the frontal bone." Sir James and Thompson exchanged glances. Dawkins stood by, a look of happiness in his eyes. His beloved camera was justifying itself once more. Inspector Wensdale breathed heavily. "Apart from all this, the position of the head on the table, and the way in which the hand was holding the pistol, not to speak of the curve of the arm, were unnatural. You get some idea of this from the photograph that Dawkins took of me, although I could only simulate death by relaxing the muscles. Again, the head would hardly be likely to twist on to its side." "The doctor ought to have seen that," said the inspector. Another thing against the theory of suicide was that the second joint of the first finger was pressing against the trigger. Mr. Challoner was an expert shot, and would instinctively have used the pad of the finger, not the second joint. "The next step," continued Malcolm Sage, "was how could anyone get into the room and approach Challoner without being heard or 'sensed.'" "He must have been very much absorbed in what he was doing," suggested Sir James. Malcolm Sage shook his head, and for a few seconds gazed at the photographs before him. "You will remember there was nothing on the table in front of him. I shall come to that presently. It is very unlikely that a man sitting at a table would not be conscious of someone approaching him from behind, no matter how quietly he stepped, _unless that man's presence in the room were quite a normal and natural thing_. That gave me the clue to Peters. He is the only person who could be in the library without Challoner taking any notice of him. Consequently it was easy for him to approach his master and shoot him." "But the locked door, sir," said Thompson. "That is a very simple matter. An ordinary lead-pencil, with a piece of string tied to one end, put through the ring of the key to act as a lever, the cord being passed beneath the door, will lock any door in existence. The pencil can then be drawn under the door. This will show how it's done." Malcolm Sage reached across for a sheet of paper, and drew a rough sketch. [Illustration] "That is why you examined the under-edge of the door?" suggested Sir James.