St. Joseph, Missouri, in 1859, is divided by a railroad track that separates the richer and poorer classes of people. From the richer side comes Ann Arnesen, daughter of Michael Arnesen, owner of the Pony Express. Michael hires Sam Cotton to protect his pony line from hostile Indians and the attacks of the gang of Peter Marquette, owner of a stagecoach line who fears losing his contracts to the pony riders. Sam finds himself in a difficult position because Michael's wife, Cathy, is in love with Marquette. Sam, despite several attacks by Marquette's men, organizes the pony line. The ailing Michael is shocked to death by his wife's confession of hate, and Marquette tries to destroy the express stations. Sam, with the aid of a friendly Indian tribe, finally wipes out Marquette and his gang, and returns to St. Joseph and Ann, the woman he loves.