A white horse and a young cowboy are the heroes in this fast-moving western about an outlaw gang led by a man pretending to be an upstanding citizen.
Three bandits attack a man and then are scared off by a wild horse. Henry Sims (Frank Hagney) says the horse Duke attacked him. A trial for the spirited horse is held on the street in front of the courtroom. The owner John Gaunt (Henry B. Walthall) asks that the horse be given another chance, and his grand-daughter Ruth (Ruth Hall) says that Duke is gentle with her. Judge Bartlett says that no one has been able to ride him, but the stranger John Drury (John Wayne) asks for the chance. The horse bucks wildly, but the young cowboy rides him until he settles down. Drury is invited to a vigilante meeting called to catch the Hawk and his gang. Drury says it is a one-man job and agrees to take it on. He is invited to a party and dances with Ruth. She tells him to be careful, because the Hawk killed her father. She asks him to ride Duke, who has chased away Drury's horse.
Henry Sims guides Drury into the desert. They show their shooting skill, and then Sims reveals he is the Hawk, tying Drury to a tree and taking his harmonica. Sims returns to his gang's ranch and plans to rob the Gordon ranch. Duke breaks free and manages to get Drury loose. The Hawk's gang sets the Gordon barn on fire and shoots a man, as Sims drops Drury's harmonica. The vigilantes go after the Hawk; finding the harmonica with JD on it, they conclude John Drury is the Hawk. They find him, but Drury says that Sims is the Hawk. The sheriff stops a hanging by taking him to "Judge Necktie Jones" at the Tequila bar. Ruth learns from the injured man that it was Henry Sims. She heads for the trial but is stopped by the Hawk's men; she cleverly says she is the Hawk's girl. The judge appoints Henry Sims as "persecuting attorney." Drury's defense is ruled irrelevant, and the jury walks out and right back in again. Ruth comes in and says that Sims was identified as the Hawk. The Hawk's men come in with guns. Sims takes Ruth hostage and dashes out, and Drury escapes with Duke. Judge Jones manages to arrest the Hawk's men with a shotgun. Sims takes Ruth to his ranch. Drury arrives, and he fights with Sims, who escapes but is cornered by Duke. The vigilantes arrive and capture the Hawk's gang. The movie ends with Drury kissing Ruth.
Animal lovers will enjoy the heroism of Duke. The film also satirizes frontier justice with the trial of a horse and a farce conducted by a hanging judge. A prominent citizen can also turn out to be a major criminal.