Plot
In 1880, teenager Mattie Ross travels to Fort Smith, Arkansas, following the murder of her father there by his hired hand, Tom Chaney. Seeking justice, Mattie hires Rooster Cogburn—an aging, alcoholic, one-eyed U.S. Marshal—to help track him down, as Chaney has fled into Indian Territory and joined the gang of outlaw "Lucky" Ned Pepper, who previously escaped Cogburn's custody. Also in town is young Texas Ranger La Boeuf, who is pursuing Chaney for the murder of a Texas senator. He offers Cogburn a share of the reward money to bring Chaney back to Texas, despite Mattie's insistence that he be hanged in Fort Smith.
Cogburn and La Boeuf set off, taking a ferry crossing with their horses and leaving Mattie behind. Undeterred, she crosses the deep river on her horse, earning Cogburn's reluctant admiration. After a failed attempt to lose her, the pair begrudgingly agree to let her join them.
Days later, the group comes across a remote cabin occupied by horse thieves Emmett Quincy and Moon. After shooting Moon in the leg, Cogburn interrogates them. Desperate for a doctor, Moon begins to talk, prompting Quincy to fatally stab him; Cogburn then shoots Quincy dead. Before dying, Moon reveals that Pepper and his gang are expected at the cabin that night for fresh horses. Cogburn and La Boeuf set up an ambush nearby. When Pepper arrives, he fires a warning shot, and La Boeuf—mistakenly thinking Cogburn has opened fire—kills Pepper's horse. A firefight ensues, in which two gang members are killed, but Pepper and the rest escape. The group brings the bodies to McAlester's store, where Cogburn tries unsuccessfully to persuade Mattie to stay behind.
One morning, while fetching water, Mattie encounters Chaney. She shoots him with her father's Colt Dragoon Revolver, wounding him and driving off his horse, but the shot draws the attention of Pepper and his gang. They take her hostage. To spare her life, Pepper orders Cogburn and La Boeuf to ride away. The gang moves on, leaving Chaney to guard her until they can replace his horse. La Boeuf, who has doubled back, warns Chaney to stand down while he and Mattie watch from afar as Cogburn engages the gang. Cogburn charges, killing two men and fatally wounding Pepper, while the last member flees. Pepper shoots Cogburn's horse, which collapses and pins him. As Pepper prepares to kill Cogburn, La Boeuf shoots him dead, but is knocked unconscious by Chaney, who attacks from behind with a rock.
Mattie fires at Chaney, but the Dragoon's recoil knocks her backward into a snake pit, where she breaks her arm and is bitten by a venomous rattlesnake. Cogburn arrives, kills Chaney, and descends into the pit to rescue her. La Boeuf helps pull them out before succumbing to his injuries. With no time to spare, Cogburn is forced to leave La Boeuf's body behind as he desperately rushes Mattie to a doctor.
Back in Fort Smith, Mattie's attorney, J. Noble Daggett, pays Cogburn his fee, and a bonus for saving her life, but warns that Mattie is gravely ill. Cogburn offers to wager the money on her full recovery, but Daggett declines. Later, Cogburn recovers La Boeuf's body and takes it to Texas for burial.
Some time afterward, he escorts the recovering Mattie back to her family ranch in Yell County, Arkansas. She tells him that, when the time comes, she wants him to be buried in the Ross family plot beside her, rather than in an unkempt, forgotten grave. Cogburn accepts, then rides off—leaping a fence to disprove her teasing remark that he is too old to jump a horse.