In 1950, “Brushy” Bill Roberts, a terminally ill old man, meets attorney Charles Phalen on a desert highway in New Mexico. Brushy wants the state governor to pardon him for killing twenty-one men in the 1870s. He identifies himself as William H. Bonney, alias the outlaw “Billy the Kid,” but Phalen reminds him that Sheriff Pat Garrett killed Billy the Kid seventy years earlier. Ignoring the comment, Brushy recalls being wounded in the leg when he, Pat Garrett, and Arkansas Dave Rudabaugh ambushed and killed a posse of vigilantes at the end of the Lincoln County War; Billy and his gang ride to Old Fort Sumner in New Mexico Territory to dress his wound at Beever Smith’s rundown hacienda. Smith informs them that Governor Lew Wallace is arresting Billy’s former gang, the “Regulators,” for prosecution. Josiah G. “Doc” Scurlock has already been taken into custody and shares a jail cell in the sheriff’s basement with fellow Regulator Jose Chavez Y Chavez and several members of “the Murphy Gang,” their enemies in the Lincoln County War. However, Billy is at the top of the governor’s “hanging list.” Fifteen-year-old orphan Tom O’Folliard asks to join the gang because he idolizes Billy the Kid, but Billy tries to dissuade him. As Pat Garrett informs Billy that Governor Wallace is in Lincoln for the trial and wants to negotiate his surrender, an old friend named Inyo tries to shoot Billy to collect the $500 reward. Billy kills Inyo, and several U.S. soldiers attack, forcing Billy to escape Fort Sumner. He arrives unannounced at Governor Wallace’s quarters and is ushered into his office. The governor offers to pardon Billy’s crimes during the Lincoln County War in return for testifying against the Murphy gang, with the proviso that Billy must then leave New Mexico. Billy agrees to be kept under guard in the comfort of a Lincoln hotel for his own protection. However, as soon as Governor Wallace leaves town, D.A. Rynerson decides to convict and hang Billy. The outlaw slips his bonds, escapes from the hotel, and sees that Chavez Y Chavez, Doc Scurlock, and the Murphy boys are jailed in the sheriff's cellar. That night, when masked vigilantes arrive to lynch the prisoners, D.A. Rynerson and Sheriff Kimbel stand aside and let them take Doc Scurlock and Chavez Y Chavez. However, as the vigilantes ride away with their captives, they pull off their hoods and reveal themselves as Billy the Kid and his gang. At that moment, a real lynch mob arrives, and a battle ensues. Billy’s gang kills most of the posse and sets half the town on fire. The next morning, Billy and Doc Scurlock fight over old slights, but Doc decides to ride with Billy’s gang to Mexico. D.A. Rynerson tells Sheriff Kimbel to bring Billy and his outlaws back, but the lawman refuses. At Beever Smith’s hacienda, Hendry William French, a farmer whose land was stolen by rancher John Simpson Chisum, joins the gang, along with young Tom O’Folliard, but Pat Garrett decides to leave and open a tavern. The gang rides to Chisum’s ranch to collect $500 he owes for past services, but Chisum defies them. When they shoot two of Chisum’s men and leave, Chisum appeals to Governor Wallace and D.A. Rynerson to exterminate Billy’s band of outlaws. They hire Pat Garrett to be the new sheriff of Lincoln County because he knows Billy the Kid’s habits and hideouts, and as an incentive, they pay him $1,000. Meanwhile, the gang rustles Chisum’s cattle. Hendry wants a nickname like the other outlaws, but Billy tells him he will have to earn one. Pat Garrett hires a local newspaper publisher, Ashmun Upson, to ride along with him and write a book about the hunt for Billy the Kid. John W. Poe and the Cattlemen’s Association join Garrett as his posse. When Billy the Kid’s gang hears news that Pat Garrett has turned against them, they continue toward Mexico. As they pass through Indian territory, Chavez Y Chavez attacks Dave Rudabaugh for vandalizing a burial ground, but the others break up the fight. To taunt Garrett, Billy leaves behind a dried buffalo scrotum on a wall that contains Garrett’s photograph with the eyes shot out. The six outlaws arrive in White Oaks, where Jane Greathouse runs a brothel. Indians surround Garrett’s posse, thinking they disturbed the sacred burial ground, but Ashmun Upson, who speaks their language, convinces them that Billy the Kid’s outlaws were the culprits. In White Oaks, townspeople form a mob to capture the gang inside the brothel, and Deputy James Carlyle goes inside to negotiate their escape in return for letting the town hang “the Indian,” Chavez Y Chavez. However, Billy disarms the deputy, dresses him with Chavez Y Chavez’s Mexican hat and blanket, and shoves him out the door. The townspeople open fire, but scatter in shame when they realize they killed their own deputy. When Pat Garrett arrives, he renews his acquaintance with Jane, but burns down her house when she defies him. Hurrying after Billy’s gang, Garrett’s posse overtakes them at a guano mine and drives them into the hills. Garrett shoots young Tom O’Folliard, but the others escape. At an abandoned adobe settlement, Billy admits to Doc Scurlock that the trail they are following does not go to Mexico after all. Accusing Billy of leading young Tom O’Folliard to his death, Doc threatens to shoot him, but changes his mind. As Doc leaves, he is killed by gunfire from Garrett’s posse. Chavez Y Chavez, Rudabaugh, and Hendry escape, but the Indian is wounded. Garrett captures Billy the Kid and returns him to Lincoln for hanging. However, Jane Greathouse slips Billy a note revealing that she has hidden a gun in the sheriff’s outhouse. There, Billy shoots both the sheriff and deputy. He secretly returns to Beever Smith’s hacienda in Fort Sumner just as Chavez and Hendry arrive and announce that Arkansas Dave Rudabaugh escaped to Mexico. Billy contemplates riding to Canada, but Chavez Y Chavez plans to stay in New Mexico because he is mortally wounded. Although Billy finally gives Hendry a moniker, “Buckshot George,” the farmer decides to return to normal life. At a town festival, Billy sees an effigy of himself hanging from a fake gallows. He spends the night with a Mexican woman, but when he steps outside in the morning, Pat Garrett confronts him. Billy tells his former friend to shoot, but Garrett, who taunts him for not going to Mexico, allows him to escape. Later, Billy the Kid’s empty coffin is buried during a funeral attended by Pat Garrett, John W. Poe, and the cattlemen. “Brushy” Bill Roberts finishes telling his story to Charles Phalen, then guides his horse into the desert.