Steve Lindsay, a civilian scout attached to the U.S. Cavalry, and his friend, Tex Harding, are assigned to investigate the murder of an Army lieutenant in connection with cattle rustling in Antelope Valley, New Mexico. After Tex and Steve ride their separate trails to Antelope Valley, Cannonball, a third scout, decides to follow them. Along the trail, Steve witnesses the holdup of a wagon driven by Sally Boylston, the niece of missing rancher Andrew Boylston. After the robber steals a legal document belonging to Sally, Steve overtakes him and escorts him to town, arriving just after Sally and her passenger, banker Henry Emerson, arrive. Jim Norton, the foreman of the Boylston ranch, who is secretly in league with the rustlers, accuses Steve of being one of the bandits. The document in Steve's possession is used to convict him, and he is sentenced to be hanged. Preparations for Steve's execution are underway when Tex and Canonball ride into town and rescue him. Later, disguising himself as The Durango Kid, a masked fighter for justice, Steve visits Sally at her ranch, and she tells him that Norton, despite the threat of the rustlers, has decided to drive a herd of cattle to an isolated Army outpost. Suspecting a setup, Steve, Tex and Cannonball disrupt the ensuing cattle raid and follow the rustlers to their hideout. There, they discover that Boylston is being held hostage, and after a shootout in which the rancher is wounded, they free him and take him to his ranch. While Sally and Tex take Boylston to the doctor in town, Steve and Cannonball decoy the bandits. Just as Steve shoots one of the rustlers, the sheriff and his posse appear. The outlaws accuse Steve and Cannonball of being rustlers, but Steve claims that Boylston can prove his innocence. The sheriff then accompanies them all to town, but when Boylston and the others fail to arrive, he jails Steve and Cannonball. After breaking out of the cell, Steve, suspecting that Norton and his henchmen are holding Boylston, Tex and Sally prisoner, dons his Durango Kid disguise and rides to the Boylston ranch to search for evidence to incriminate Norton. Upon finding a damning bank book in Norton's name, Steve confronts him with the evidence and threatens to turn him over to the authorities unless Norton gives him half of his ill-gotten gains. Norton consents and leads Steve to his hideout, where a blazing gunfight ensues between Steve and the outlaws. Just in the nick of time, Cannonball and the sheriff arrive to apprehend Norton and his henchmen and bring them to justice.