Michael Arnesen (Reinhold Schünzel), head of the Pony Express, receives reports from his riders of widespread attacks by Native Americans and jealous business rivals alike. Arnesen hires Sam Cotton (William Elliott) to ensure the success of the Express. Cotton must face Peter Marquette (Joseph Schildkraut), a vicious man desperate to keep his failing stagecoach line afloat -- no matter the cost. And in the midst of danger, Cotton falls for Arnesen's daughter Ann (Vera Ralston).