In 1880 in Yell County, Arkansas, 14-year-old Mattie Ross vows vengeance on her father's murderer, hired man Tom Chaney, who has fled into Indian Territory. Accordingly, she enlists the aid of one-eyed U. S. Marshal Rooster Cogburn and accepts the help of Texas Ranger La Boeuf, who is intent on the reward awaiting the man to capture Chaney for crimes committed in Texas. Despite mutual distrust, Rooster and La Boeuf unite to dissuade Mattie from accompanying them on their dangerous mission. Undeterred, she joins the manhunt. The trio tracks the assassin across the border to the refuge of outlaw Ned Pepper. During a surprise raid on Pepper's hideout, the lawmen kill four of his fellows and find a gold piece once the property of Mattie's father. Alone, Mattie encounters Chaney. Although she wounds him, Mattie is taken hostage by Pepper's band. Fearing for the girl's life, La Boeuf and Rooster pretend to retreat. Armed to the teeth, the two return unexpectedly to rescue Mattie. As Chaney bludgeons La Boeuf, Mattie shoots the fugitive a second time and falls backwards into a snakepit. After slaying Chaney, Rooster, aided by the dying ranger, pulls Mattie from the pit. Discovering that she has been bitten by a rattlesnake, the marshal, himself wounded, rushes the girl to a physician. Recovering from her injuries, the child proclaims to Rooster her wish to be buried next to him.