"Really, Major, you seem to have made a speciality of detective fiction. As you said, I suppose your theory is possible." Jesson spoke casually, but his eyes for the first time left the face of the man opposite him and roved towards the door. For the first time a sudden ghastly suspicion of the truth entered the Sapper's brain; and even as it did so he noticed that Staunton's revolver--the cleansing finished--pointed steadily at Jesson's chest. "I am glad you think it possible. To render it probable we must go a bit farther. The essence of all detective stories is the final clue that catches the criminal, isn't it?" The revolver moved an inch or two farther into prominence. "Good Lord, Dickie? Is that gun of yours loaded?" cried the Adjutant in alarm. For the first time he also seemed to become aware that something unusual was happening, and he suddenly stood up. "What the devil is it, Major? What have you got that gun on him for?" "For fun, dear boy, for fun. It's part of the atmosphere. We've got to the point haven't we, where--in my story, of course--the German dressed in Brinton's uniform comes into the English lines. Now what sort of a man would they send in this part of the line, where mining activity is great? I continue the theory, you see; that's all." He looked at Jesson, who made no reply; though without cessation he moistened his lips with his tongue. "A miner." The Adjutant's voice cut in. "Go on, for God's sake." "Precisely--a miner. The second point of detail; and two points of detail are a strange coincidence--nothing more. Only--there is a third." "And three are a moral certainty, as you've often said." The Adjutant once again bent across the table and spoke softly. "Are you fooling, Dickie--are you fooling? If so, the joke has gone far enough." But the Sapper's eyes were fixed on a leg that twitched, and they wandered now and then to a neck where--even in the dim light of a candle--he could see a pulse throbbing--throbbing. "It's not a joke," he said, and his mouth was dry. "What is the third point of detail, Dickie?" "Yes, what is the third point of detail, sir?" Jesson's voice was steady as a rock. "I am very interested in your problem." He raised his hands from the table and stretched them in front of him. Not a finger quivered, and with a sublime insolence he examined his nails. To the Sapper there occurred suddenly those lines of Kipling, "For there is neither East nor West, border nor breed nor birth, When two strong men come face to face though they come from the ends of the earth." He _knew_ now; he realised the man beside him was a German; he knew that the sentence of death was very near. What the clue was that had given the man away he hardly thought about--in fact, he hardly cared. All he knew was that death was waiting for the man beside him, and that his hands were steady as a rock.