Mort Bemis gave Jack Knight a revengeful look. Then he moved towards the trap in the floor.

The scene was the depot switch tower at Stanley Junction, in sight of the local passenger depot. It loomed up thirty feet in the air, glass-windowed on every side. It was neat, light, and airy. In its center, running nearly its length, was the row of long heavy levers that controlled the depot and siding switches of the terminus of the Great Northern Railroad.

The big-framed, business-faced man who bustled among these, keeping an angry eye meantime on an unwelcome visitor, was a veteran and a marvel in local railroad circles.

When the Great Northern had come to Stanley Junction, ten years back, it brought old Jack Knight with it,

He had an eye like an eagle and the muscles of a giant. The inside of his head was popularly believed to be a vast railroad map. He controlled the main rails, switches, and sidings, like a woman would the threads of an intricate knitting piece. He directed the locomotives and trains up and down that puzzling network of rails, like puppets moved by strings. In ten years' service he had never been responsible for an accident or a wreck.

Old Jack, therefore, having never made a mistake in railroading, had little patience with the careless, lazy specimen whom he had just ordered out of the place.

Mort Bemis had been his assistant in the tower. The fellow's record had always been full of flaws. He was slow and indifferent at the levers. He associated with a shiftless crowd outside. He borrowed money and did not pay it back. He was unreliable, disagreeable, and unpopular.

Three days previous, old Jack was adjusting a heavy weight bar on the lower story of the switch tower.

Mort, upstairs, was supposed to safely hold back a spring-bar apparatus while his superior was fixing the delicate mechanism below.

His mind everywhere except on his task, Mort for an instant took his hand off the bar to wave a recognition to a chosen chum, "flipping" a passing freight train.