A wagon load of powder explodes, destroying the railroad trestle under which it is passing; Helen, knowing that a passenger train is due within a few minutes, climbs aboard a freight car which coasts down a steep grade near the trestle. As it nears the structure, she applies the brakes, leaps to the ground, crawls across the burning trestle and over the single remaining rail to the other side, where she flags the train just in time to prevent an accident.