A rigid investigation was ordered at once, but no clue to the perpetrator of the mischief was discovered. Yet it seemed certain that it could not have been done by a tramp. No tramp had been in the yards—the yard-men were sure of that—and the officials were forced to the unwelcome conclusion that some one whom they did not suspect—some one who was permitted to enter the yards—some one connected with the road, perhaps—was guilty. It was a disquieting thought, for there was no telling what might happen next. And then, one morning, Allan solved the mystery. It was a little after four o’clock and still quite dark as he passed through the yards to start on his morning walk. A freight-train stood ready to start east, with its great mogul of an engine puffing and blowing with impatience. Just as Allan passed it, he saw a figure emerge from underneath it. He thought at first it was the engineer, but, instead of mounting to the cab, the figure slunk away into the darkness, carefully avoiding the glare of the headlight. Then the boy saw the conductor and engineer standing, with heads together, a little distance away, reading their orders by the light of the conductor’s lantern. He ran toward them. “Mr. Spurling,” he said to the engineer, “I just saw a man come out from under your engine.” “You did!” and engineer and conductor, with compressed lips, hurried back to where the engine stood. The former flashed his torch underneath, and then straightened up with a very grim face. “Look at that link-motion,” he said, and the conductor stooped and looked. Then he, too, straightened up. “It’s a good thing we didn’t get started,” he said. “I’ll go and report it. It’s lucky for us you saw that scoundrel, my boy,” he added, as he hurried away, and the engineer clapped Allan on the shoulder. “Mighty lucky,” he said. “It’s a good thing there’s one man around here who keeps his eyes open.” But Allan, as he started away at last upon his six-mile tramp, knew not whether to be glad or sorry. If only some one else had passed the engine at that moment instead of him. For, as that crouching figure slunk away through the darkness, he had recognized it! So he had a battle to fight on that six-mile tramp; but it was fought and won long before the walk was ended. And when, at last, he got back to the yards, instead of turning away toward home, he mounted the stairs to the train-master’s office. That official was busy, as always, with a great pile of correspondence, but he looked up and nodded pleasantly as Allan entered. “Good morning, West,” he said. “Want to speak to me?” “Yes, Mr. Schofield,” answered Allan. “This morning, as I was starting out on my trick, I saw a man come out from under Mr. Spurling’s engine.” The train-master nodded. “Yes,” he said, “I’ve got a report of it here. I’m mighty glad you happened to come along just when you did, and had your eyes about you.”