In southern Arizona territory, former hired gun-turned-marshal Chris Adams rescues his old friend, former bounty hunter Jim Mackay from an ambush. After recovering from his long ride across the desert, Jim asks Chris to help him defend the small Mexican border town of Magdalena, which has come under constant attack by bandit De Toro and his men. Having recently married and assumed his job as marshal, however, Chris is reluctant to assist Jim, despite their long friendship. Later, Chris refuses the request of his wife Arrila to release jailed teenager Shelly Donavan, who is charged with robbery, insisting that Donavan needs to be responsible for his actions. Chris then meets with newspaper writer Noah Forbes who wants to write the story of Chris's eventful and brutal career. The next morning, while loading bitter prisoners Pepe Carral, Walt Drummond and Donavan onto the Tucson prison wagon transport, Chris abruptly decides to let Donavan go free. While Chris meets Noah to discuss his exploits, Donavan joins his friends, brothers Hank and Bob Allen to celebrate his release. Goaded into action by the Allens' observation that their drab lives as farmers remain unchanged, Donavan leads the pair in a bank robbery just as Arrila meets Chris and Noah in the street outside the bank. Wounding Chris, Donavan abducts Arrila and rides away with the Allens. Reviving two days later, Chris immediately goes in search of Arrila, despite his injury, and agrees to let Noah accompany him. In the desert, Noah and Chris find Arrila's dead body, which galvanizes Chris to find Donavan and exact revenge. That night, Chris tracks down the Allens and demands to know Donavan's whereabouts. Confident that Chris, as marshal, must take them back to town for a trial unharmed, Hank reveals that Donavan has fled to Mexico and admits that Arrila was raped and tortured before her murder. Chris shoots Hank, and Bob, pleading for his life, insists that he did not join in the assault. Accusing him of allowing Arrila's attack, Chris then shoots Bob as Noah looks on in shock. Continuing his search for Donavan, Chris rides on toward the Mexican border and finds Jim with a group of armed farmers from Magdalena hiding on a ridge, hoping to ambush De Toro. After Jim reveals that Donavan rode by the previous day, he again asks Chris to support him, but Chris refuses and tells his friend he is badly outnumbered and will be slaughtered. Chris and Noah depart, tracking Donavan through the desert, only to find themselves circling back toward Jim's location. Hearing distant gunfire, the men hurry to the ridge, but find the farmers dead, although Jim is not among them. Chris reflects that the men of Magdalena have likely left their wives unprotected and, assuming Jim will have returned there, rides into Mexico with the uncertain Noah. Arriving in Magdalena, Chris spots three bandits around the mission and after shooting them, enters the church to find the handful of townswomen who have been raped and beaten. Laurie Gunn explains that the seventeen women were defenseless against De Toro and his more than forty men who arrived the previous day declaring the women's husbands had been massacred. Although Laurie and the women plead with Chris to take them away from Magdalena 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 wonders how to defend the women. Promising to return to help the frantic women, Chris and Noah ride away toward Tucson. Not far from Magdalena, the pair come upon the bodies of Jim, Donavan and the remaining farmers. At Tucson, Chris meets with the governor then travels to the prison where he presents the skeptical warden with a request to pardon the last five prisoners he arrested, all of whom are tough, violent men: Carral, Drummond, Scott Elliot, Mark Skinner and former Confederate captain Andy Hayes. Meeting the men, Chris explains he will sign their pardons only if they agree to join his posse. Although suspicious and hostile, the men grudgingly agree. Loaded with supplies from the prison, the group departs for De Toro's hacienda, which Jim had described earlier. Arriving just outside of the hacienda and confirming that only a few men are posted as guards, Chris tells the men to raid the house and take anything they desire. Although doubtful, the men agree and quickly overcome the guards and loot the home. Finding De Toro's woman there, Chris orders her taken captive and as the men ride off to Magdalena, Chris tells the men that if they try to escape before he signs the pardons, they will be hunted in America and De Toro will hound them through Mexico for destroying his home. Realizing they have no alternative, the men give up their ideas of breaking away in Mexico and continue to Magdalena where Laurie and the grateful women wait. Suspecting they may have only a day to prepare before De Toro tracks them, Chris designs an elaborate plan of attack using the supplies of long-range rifles, dynamite, barbed wire and repeating rifles. The next day with the women's assistance and under former construction worker Elliot's guidance, the group digs several ditches, building several post and barbed wire fences at specific points leading back into the town. Elliott also constructs hidden barriers across mountain trails into the town. The following day, with the women trained in reloading the weapons, the group awaits De Toro's arrival. When the bandits attack, the initial assault with the long-range guns, sends the outlaws into disarray. Chris and the others retreat as planned to the second line of defense, which, protected by Elliot's clever rigged barbed fence, cuts off another large segment of the bandits who are then dynamited. Drummond and Hayes are shot down and Noah wounded as the group retreats into the town behind another rigged barricade. During a brief lull, Chris goes into the mission where De Toro's woman and the town children are being kept, and tells Laurie that as a last resort they will lure the bandits inside and blow up the church. When De Toro's renewed assault comes, Carral and Elliot are killed. Hearing the bandits approaching the mission, Laurie prepares to detonate the dynamite, but first sets De Toro's woman free. The woman rushes outside into the gunfight and is accidentally shot down by De Toro himself. Momentarily stunned, De Toro pauses, and Chris kills him. Dismayed by the death of their leader, the remaining bandits ride away. Relieved to have survived, Chris, Noah and Skinner agree to stay in Magdalena and start new lives.