In southern Arizona Territory, hired gun-turned-marshal Chris Adams rescues his old friend, former bounty hunter Jim Mackay, from an ambush. Jim asks Chris to help him defend the Mexican border town of Magdalena from De Toro and his bandits, but Chris is reluctant.
Chris refuses his new wife Arrila's request to release teenager Shelly Donavan, jailed for robbery. Chris meets with newspaper writer Noah Forbes for a story on Chris' eventful career.
The next morning, loading prisoners onto the Tucson prison wagon, Chris decides to free Donavan. Chris meets Noah to discuss his exploits, as Donavan celebrates his release with Hank and Bob Allen. Donavan leads the brothers in a bank robbery just as Arrila meets Chris and Noah outside. Wounding Chris, Donavan abducts Arrila and escapes with the Allens. Revived two days later, Chris sets off in search of Arrila, accompanied by Noah.
In the desert, Noah and Chris find Arrila dead. Chris tracks down the Allens and demands to know Donavan's whereabouts. Confident that Chris will take them back to town for trial and not shoot them on the spot, Hank refuses to talk. Chris shoots him. Bob then decides to talk and reveals that Donavan has fled to Mexico, and admits Arrila was raped and tortured before her murder. Bob pleads for his life, insisting he did not join in the assault, but Chris shoots him (for not preventing it, either) as Noah looks on in shock.
Chris rides to the Mexican border and finds Jim with armed farmers from Magdalena, hoping to ambush De Toro. Jim reveals that Donavan rode by the previous day, and Chris again refuses to join, telling Jim he is badly outnumbered and will be slaughtered. Chris and Noah track Donavan through the desert, only to find themselves circling back toward Jim's location. Hearing distant gunfire, they find the farmers dead with no sign of Jim. Chris assumes the women of Magdalena have been left unprotected and Jim will have returned there, and rides into Mexico with the uncertain Noah.
At the mission in Magdalena, Chris kills three bandits and find the townswomen, who have been beaten and raped. Laurie Gunn explains that the women were defenseless against De Toro and his more than forty men who arrived the previous day. Although Laurie and the women plead with Chris to help them escape before De Toro's return, he points out there are no horses and a desert trek would kill them. Realizing that the American Cavalry will not cross the border, Chris and Noah ride to Tucson, promising to return. Not far from Magdalena, the pair come upon the bodies of Jim and Donavan (with McKay having avenged Shelly's betrayal of the ambush to DeToro's gang).
In Tucson, Chris meets with the governor then travels to the prison, asking the warden to pardon the last five prisoners he arrested: Pepe Carrall, Walt Drummond, Scott Elliott, Mark Skinner, and former Confederate captain Andy Hayes. Chris tells the criminals he will sign their pardons if they join his posse, and they grudgingly agree. Loaded with supplies, the group departs for De Toro's hacienda. The men overcome the guards and loot the home, and Chris takes De Toro's woman captive. Riding to Magdalena, Chris warns the men not to escape.
Chris designs an elaborate trap for the bandits. The women and construction worker Elliott help prepare several ditches, barbed wire fences, and hidden barriers. After training the women in reloading the weapons, the town awaits De Toro's arrival. The bandits attack, but the town's initial assault with long-range guns sends the outlaws into disarray. The defenders retreat to the second line of defense; protected by Elliott's clever fences, they dynamite many of the bandits. Walt, Hayes and Elliott are killed and Noah wounded as the group retreats behind another rigged barricade.
At the mission where De Toro's woman and the town children are hiding, Chris tells Laurie his last resort: they will lure the bandits inside and blow up the church. Pepe is killed in De Toro's renewed assault. Hearing the bandits approach, Laurie prepares to dynamite the mission and frees De Toro's woman, who rushes outside into the gunfight and is shot by De Toro. Momentarily stunned, De Toro is killed by Chris, and the remaining bandits flee.
Chris, Noah, and Skinner decide to start new lives in Magdalena.
