"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.