Jim, determined to ruin a box car brake test, hides inside, removes the flooring, and ruins the brake apparatus. As a result, the box car runs wild, trapping him inside. Before Helen can sidetrack the runaway, it shoots off the track at Elbow curve, overturning as it topples down the embankment. Helen smashes a hole through the side, braves the flames, crawls into the car, rescues Jim and drags him to safety. But her heroism is too late; Jim dies in her arms.
