An express train was on its way from London to Edinburgh. It was running at sixty miles an hour, and the passengers, as comfortable as if they had been sitting in easy chairs by their own firesides, were engaged in reading, sleeping, talking or looking out of the windows. Not a thought of any impending trouble crossed their minds.<br><br>Suddenly they felt a jar, followed by a jerk; the train slowed down, and within ten seconds had come to a standstill. Then there was general commotion, and heads appeared at every window, to see or inquire what was the matter. There was no station in sight, and no signal against them. Yet that train, which a few moments earlier had been speeding along in all its power and pride, had come to a dead stop.<br><br>And when those passengers alighted from their compartments and began to investigate matters, they were no nearer a solution of the mystery.