The order was carried out briskly, and when the oddly made up train slowed to a stand beside the bunk car, the pick-handle squad climbed upon the rearward car, and the chief and his first assistant sprang into the engine cab. “Down the line!” was David’s order to the engine-driver, and the train moved off, gathering such momentum as the roughly surfaced construction track permitted. In the make-up of the train the engine was backing, with an empty flat-car for its pilot. Being a construction machine, the locomotive had a headlight at either end. With the yard switches left behind, David reached up, uncoiled the short signal-bell cord, and shouted into the ear of the big Irishman at the throttle. “Listen, Callahan: I’m going up on the coal to keep a lookout and flag for you. If I give you one bell, clamp your brakes and make an emergency stop; if I give you two bells, let her have all she will take. Understand?” The Irishman nodded; and David, with Plegg at his heels, climbed over the coal to a lookout position on the rear end of the tender. By this time the scenery, or so much of it as the starlight revealed, was unreeling itself rapidly on either hand, and in the beam of the tender-carried headlight the straight-away stretches of the track rushed up in quick succession to be shot to the rear under the roaring wheels. “Lord!” yelped Plegg; “if we should meet ’em on a curve!----” but David Vallory made no reply. He was gripping the bell-cord and staring steadily down the track ahead, following the double line of rails to the farthest reach of the spreading cone of light. As it chanced, the meeting point with the gasoline-driven push-car was not on a curve. On the mile-long tangent which marked the approach to bridge Number Three the converging lines of the rails in the distance met in a dark blot; a moving blot that shot quickly into the glare of the headlight. Plegg saw a series of black dots tumbling grotesquely from the blot to right and left, heard a sharp double clang of the signal in the cab behind him, and felt the sudden lurch of the tender as the engine’s throttle was opened. “_Duck!_” was the command shouted in his ear, and the next instant there was a crash and the air was filled with flying wreckage. Luckily, no wheel of the attacking train was derailed, and a minute or so later, Callahan, in obedience to a signal from his chief, was braking the heavy “mogul” to a stop beside Crawford’s dynamited rock pile. The place was light with flares, the concrete-pouring on the bridge had been resumed, and Crawford came down the staging runway with a broad grin on his boyish face. “I saw a little of it from the far end of the staging,” he chuckled. “How many of ’em did you get?” “Not any of them, I hope,” said David Vallory soberly, as he swung down from the engine step. “It was meant for an object-lesson--not a murder. Now talk fast, Crawford: how many of them are there, and who are they?--besides Lushing?”