In the 1870s, a train carries a varied assortment of passengers through America's frontier mountains, en route to a remote army outpost. Accused arsonist and thief John Deakin (Charles Bronson) is being escorted by a corrupt US Marshall (Ben Johnson), while a territorial governor (Richard Crenna) is attempting to conceal an adulterous affair with his lady companion (Jill Ireland). The tensions bubble to the surface when a murder is committed and the finger of suspicion is, by turns, pointed at each of the train's passenger.