In the small border town of Sinola, New Mexico, the local judge is in the midst of sentencing rancher Joe Kidd to ten days in jail for drunk and disorderly conduct and poaching when a band of Mexican Americans, led by Luis Chama, bursts into the courtroom to protest the theft of their land by Anglos. Charging that their legitimate deeds were deliberately destroyed in a fire, thus making their claims unprovable, Chama grabs the Anglo deeds piled on the judge's podium and lights them on fire. Quickly taking the judge out of the courtroom, Joe escorts him to the saloon and instructs him to leave through the back door. Soon after, Naco, one of Chama's men, enters the saloon looking for the judge, and when he draws his gun on Joe, Joe levels a shotgun at him and kills him. The town's ineffectual sheriff, Bob Mitchell, forms a posse to pursue Chama, but Joe refuses to join them because he has no grievance against him. When Mitchell and his posse return to town empty-handed, Joe begins serving his ten-day sentence. Shortly thereafter, a train brings land baron Frank Harlan, his mistress Elma and his sharpshooters, Roy Gannon, Olin Mingo and Lamarr Simms, to town. After checking into the hotel, Harlan pays Joe's fine and instructs the sheriff to send him over for a meeting. Claiming that his heavily armed party is interested in hunting, Harlan offers Joe $500 to guide them into the mountains. Joe, who before becoming a rancher was a fearsome bounty hunter, senses that Harlan's quarry is Chama, and so refuses the offer and instead rides back to his ranch. When he finds that Chama and his men have stolen his horses and injured his loyal ranch hand Emilio, however, Joe rides back to town and offers to serve as Harlan's guide for $1,000. As the motley band threads their way along the mountain trails, they are stopped by several of Chama's men, who are leading Joe's stolen horses. When the men refuse to divulge Chama's whereabouts, Harlan instructs his sharpshooters to wound the leader and kill the rest. After the leader still refuses to cooperate, Harlan cold-bloodedly orders the defenseless man killed. Soon after, they come upon a shack owned by Helen Sanchez. Although Joe recognizes Helen as one of Chama's gang that invaded the courtroom, the others are unaware of her allegiance. Desirous of sharing Helen's bed, Harlan decides to set up camp there for the night. In a moment alone with Helen, Joe reassures her that he will not disclose her association with Chama. Helen is contemptuous of Joe for his relationship with Harlan, and when he asks her about Emilio, she replies that Ramon, one of the gang, made sure that he would not follow them. The next morning when they leave camp, Harlan takes Helen with them, and soon after, meets another contingent of his men led by Eljay. As they reach a small Mexican village at the base of the mountains, Chama and his men open fire on them from the hills above. In response, Harlan takes the villagers hostage, orders them to pile their decrepit weapons on a table and informs Chama that he has until the next morning to surrender, or five of the villagers will be executed. After Harlan informs Joe that he is fired, the trigger-happy Lamarr, who wields a deadly, custom-made gun, points to the villagers' pile of weapons and challenges him to draw. After smashing Lamarr in the throat with a rifle butt, Joe enters the church to join the hostages. There Helen asserts that Chama, as a man of the people, will surely come to their rescue. Upon recovering from the blow to his throat, the hoarse Lamarr takes watch on the bell tower above the church. Peeping through the trap door leading to the tower, Joe pulls it open just as Lamarr steps on it, sending Lamarr plunging to his death on the church floor below. Taking Lamarr's fancy weapon, Joe scales down the tower. After sneaking into Harlan's room, Joe grabs Harlan's high-powered rifle just as Chama's deadline passes and Harlan orders five villagers to be lined up and shot. Pulling Helen outside with him, Joe opens fire on the executioners, then rides off with Helen and frees Harlan's horses, thus preventing him from following. Upon reaching Chama, the now disillusioned Helen lashes out at him for allowing the villagers to die and accuses him of being interested only in himself. Suggesting that Chama return to Sinola with him, Joe pulls out his gun to make his point, then yells down to Harlan that Chama can be found at the Sinola jail. After gathering their horses, Harlan and his men engage in a skirmish with Joe, then continue to town, where Harlan stations his sharpshooters along the rooftops, waiting for Joe to arrive. On the outskirts of town, Chama dismisses his men, but Joe orders Ramon to stay with them. Sensing an ambush, Joe tells Ramon to ride in first, and after Ramon is shot off his horse, the others turn around and board an empty train that is idling on the tracks just outside town. Commandeering the engine, Joe drives the train past the station and into the saloon in which Harlan's sharpshooters are drinking. From his hotel window, Harlan fires at Joe, then runs into the street to take cover in the courthouse. After Harlan's men surrender, Joe instructs Helen, Chama and the bartender to cover him while he follows Harlan into the courthouse. When Harlan enters the chambers, he finds Joe seated in the judge's chair. With a glint in his eyes, Joe pulls the trigger of his gun, killing Harlan. After turning Chama over to the sheriff, Joe knocks the inept lawman down in disgust, then rides off to his ranch with Helen.
