In late 1890s Wyoming, Butch Cassidy is the affable, clever, talkative leader of the outlaw Hole in the Wall Gang. His closest companion is the laconic dead-shot "Sundance Kid". As the west rapidly becomes civilized, the law finally catches up to Butch, Sundance and their gang. Chased doggedly by a special posse, the two decide to make their way to South America in hopes of evading their pursuers once and for all.
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.