A pioneering agent of the express delivery company opens a new route from St. Louis to San Francisco and delivers gold during the Civil War.
Ramsay MacKay (Joel McCrea) brings mail and refuses to be arrested for competing with the government. He picks up stranded Justine Pryor (Frances Dee) and her mother (Mary Nash), hurrying to deliver fresh oysters to Henry Wells (Henry O'Neill) in Buffalo for banker Bradford. In St. Louis Nicholas Pryor (Ralph Morgan) waits for a shipment from Wells and Fargo. His daughter Justine thanks Ramsay with a kiss.
In 1846 Ramsay has an office and greets Wells, who wants a route to California. At a dance Talbot Carter (Johnny Mack Brown) courts Justine; but she and Ramsay want to marry. Justine asks to go with Ramsay to California and kisses him good-bye. In 1850 San Francisco Ramsay sees men waiting hours for mail. He sorts and delivers mail to some miners and tells Hank York (Bob Burns) he made $500 on one trip. Dan Trimball (Robert Cummings) asks Ramsay to send gold dust to St. Louis for his fiancé to come. Two robbers shoot Ramsay and take his gold shipment. Ramsay recovers and tells men he will pay for their losses.
In 1851 a ship arrives with Wells, John Butterfield (Clarence Kolb), and Dan's fiancé. Ramsay finds Justine, and they get married. Ramsay goes to miners. Dan tells him his wife needs a doctor. Dan's wife dies, and Ramsay hires Hank to take the baby to St. Louis. Ramsay comes home to find Justine had her baby. In 1857 Ramsay is put in charge of laying out the overland route; he promised Justine he would not leave San Francisco, but she lets him go. Wells tells Butterfield they must make it from Missouri in 25 days, or the contract is canceled. Ramsay, Butterfield, and Hank find five massacred at a way station, and later they shoot and flee Indians. San Francisco welcomes Ramsay. The Pony Express brings news in ten days, and telegraph lines reach Nevada in 1860.
Confederate soldiers seize gold shipments. President Lincoln tells Ramsay he must deliver the treasury from San Francisco. Ramsay calls on the Pryors, whose son was killed in Georgia. Mrs. Pryor goes to help Justine with her second child. Justine writes a letter about the route but throws it away. Ramsay encounters Confederate troops led by Talbot, who demands the gold. In the shooting battle all the Confederates are killed, and Ramsay finds Justine's letter. Justine sails with her mother.
Years later Justine lives with her father. At a banquet Wells and Hank honor Ramsay with a gold plaque. Ramsay finds at home his daughter Alice (Peggy Stewart), who invites him to her birthday party. There he talks with Justine and gives her the letter. Justine says she threw it away, and both realize that her mother must have sent it.
This drama conveys how one pioneer helped Wells Fargo develop its business and improve transportation in the West, and it also indicates the conflict within a family during the Civil War; both career and the war caused separations between a man and a woman who loved each other.