The defense and the prosecution have rested and the jury is filing into the jury room to decide if a young Spanish-American is guilty or innocent of murdering his father. What begins as an open and shut case soon becomes a mini-drama of each of the jurors' prejudices and preconceptions about the trial, the accused, and each other.
The murder of her father sends a teenage tomboy, Mattie Ross (Kim Darby), on a mission of "justice", which involves avenging her father's death. She recruits a tough old marshal, "Rooster" Cogburn (John Wayne), because he has "grit", and a reputation of getting the job done. The two are joined by a Texas Ranger, La Boeuf (Glen Campbell), who is looking for the same man (Jeff Corey) for a separate murder in Texas. Their odyssey takes them from Fort Smith, Arkansas, deep into the Indian Territory (present day Oklahoma) to find their man.