A mail-order bride enlists an outlaw and a mystery man to help protect her land from a ruthless cattleman.

In the West during the 1870's, Frank, a ruthless killer, sends three of his henchmen to a remote railway depot to wait for The Man, an impassive gunman whose trademark is playing sad songs on a harmonica. The Man guesses their murderous intent when they refuse to answer a question about Frank, and he kills them before they can reach for their guns. Meanwhile, rancher Brett McBain and his three motherless children await the arrival of Jill, a New Orleans prostitute whom Brett has recently married. Suddenly, Frank and his gang appear and gun down Brett and the children. They plant evidence implicating Cheyenne, a notorious half-breed. Arriving at the ranch, Jill finds a burial service being conducted and learns that McBain's promise of wealth was for the future when his property, through which a new railroad must pass, would become the center of a thriving community. Too frightened to remain in the area, Jill is forced to auction off her property. Frank, who is employed by Morton, a crippled railroad executive, tries to fix the sale, but The Man appears with Cheyenne in tow and buys the land for $5,000--the exact amount of the reward money for capturing Cheyenne. The Man then returns the land rights to Jill but refuses to explain his actions. A short time later, he rescues Frank from an ambush by his own men who had sold their loyalty to the double-crossing Morton. The Man still refuses to explain his motives or reveal his true identity to Frank, but he returns to the ranch to help Jill with the work and to protect her from Frank. Cheyenne, who is now on friendly terms with The Man, also arrives after being cleared of the McBains' murders. He has been wounded in a gunfight with Morton's men. Frank eventually shows up to face The Man in a gun duel, and he is shot before he has time to draw his gun. Before Frank dies, The Man explains to him the reason for the vendetta: when The Man was 15 years old, Frank forced him to play the harmonica while his older brother was tortured and hanged. With his mission accomplished, The Man says goodby to Jill and rides off with the mortally wounded Cheyenne. Alone at the ranch, Jill distributes water to the men who are helping to build the new railroad town.