Joe Kidd is a former bounty hunter and all-around tough-guy in the American Southwest during the Mexican-American War.
When a band of Mexicans find their U. S. land claims denied and all relevant records destroyed in a courthouse fire, they turn to force of arms. Louis Chama is their charismatic leader, spouting revolutionary rhetoric and demanding land reform.
A wealthy landowner with interests in the disputed area, Frank Harlan, decides to settle things his own way. He hires a band of killers and wants Joe Kidd to help them track Chama. Initially, Kidd wants to avoid any involvement, until Chama makes the mistake of stealing Kidd's horses and terrorizing his friends.