"It is really too elementary, Whatson, but I am always willing to oblige a friend. I shall be relieved, however, when you are able to work out the A B C of detection for yourself, although I shall never object to helping you with the words of more than three syllables. Having made up his mind to commit suicide, Kipson naturally intended to do it before he reached Brewster, because tickets are again examined at that point. When the train began to stop at the signal near Pegram, he came to the false conclusion that it was stopping at Brewster. The fact that the shot was not heard is accounted for by the screech of the air- brake, added to the noise of the train. Probably the whistle was also sounding at the same moment. The train being a fast express would stop as near the signal as possible. The air-brake will stop a train in twice its own length. Call it three times in this case. Very well. At three times the length of this train from the signalpost towards London, deducting half the length of the train, as this carriage is in the middle, you will find the pistol." "Wonderful!" I exclaimed. "Commonplace," he murmured. At this moment the whistle sounded shrilly, and we felt the grind of the air-brakes. "The Pegram signal again," cried Kombs, with something almost like enthusiasm. "This is indeed luck. We will get out here, Whatson, and test the matter." As the train stopped, we got out on the right-hand side of the line. The engine stood panting impatiently under the red light, which changed to green as I looked at it. As the train moved on with increasing speed, the detective counted the carriages, and noted down the number. It was now dark, with the thin crescent of the moon hanging in the western sky throwing a weird half-light on the shining metals. The rear lamps of the train disappeared around a curve, and the signal stood at baleful red again. The black magic of the lonesome night in that strange place impressed me, but the detective was a most practical man. He placed his back against the signal-post, and paced up the line with even strides, counting his steps. I walked along the permanent way beside him silently. At last he stopped, and took a tapeline from his pocket. He ran it out until the ten feet six inches were unrolled, scanning the figures in the wan light of the new moon. Giving me the end, he placed his knuckles on the metals, motioning me to proceed down the embankment. I stretched out the line, and then sank my hand in the damp grass to mark the spot. "Good God!" I cried, aghast, "what is this?" "It is the pistol," said Kombs quietly. It was!! * * * * *