Marshal Wyatt Earp kills a couple of men of the Clanton-gang in a fight. In revenge Clanton's thugs kill the marshal's brother. Thus, Wyatt Earp starts to chase the killers together with his friend Doc Holliday.
Earp agrees to become marshal and establish order in Tombstone in this very romanticized version of the gunfight at the O.K. Corral (e.g., Doc is killed by Curley before the actual battle and Earp must do the job alone).