Also, civilian passengers are on the train in the rear luxurious private car – Nevada Governor Fairchild (Richard Crenna) and his fiancée Marica (Jill Ireland), the daughter of the fort's commander.

Deakin, who is actually an undercover U.S. Secret Service agent, uncovers en route that the "epidemic" at the outpost is actually a conspiracy between a group of killers led by the notorious outlaw Levi Calhoun (Robert Tessier) and a tribe of Native Americans under Chief White Hand (Eddie Little Sky).

Instead of medical supplies, the train's boxcars are transporting a large secret shipment of firearms, ammunition and dynamite stolen from U.S. manufacturers for sale to the Natives, in return for allowing Calhoun and his men to mine and smuggle gold from their lands.

Most of the people on the train, including Governor Fairchild and Marshal Pearce, are Calhoun's partners in crime, and those innocents who discover the evidence for his sinister plot are eliminated.

Eventually, Deakin narrows his list of possible uninvolved allies down to Marica and Army Major Claremont (Ed Lauter), who agrees to assist the agent in his efforts to prevent the arms delivery.

Producers Elliott Kastner and Jerry Gershwin had filmed a number of Alistair MacLean novels previously, including Where Eagles Dare and When Eight Bells Toll.

[10] Opening scenes in the Myrtle settlement / "whistle stop" were shot at a specially built set (to look like an old abandoned gold-rush town) just outside Arrow Junction, about fifteen miles (25 km) east of Lewiston.

[21] In the Los Angeles Times, critic Kevin Thomas called it, "a fun if familiar picture, but is played so broadly on such an elementary level that it can hope to satisfy only the most undemanding of viewer.