A prequel of sorts to Butch Cassidy and the Sundance Kid (1969) which chronicles the two outlaws' lives in the years before the events portrayed in the 1969 movie.

The early partnership of outlaws Robert LeRoy Parker and Harry Alonzo Longabaugh, better known as Butch Cassidy and the Sundance Kid, in the late nineteenth century American frontier is told. Just paroled from a Wyoming prison on a vow to the state's Governor, affable and otherwise honorable Butch returns to his old stomping grounds of Brown's Hole, Utah, where he meets Longabaugh in a casino shootout gone wrong, the event initiated by Longabaugh. Despite baby-faced and more volatile Longabaugh not looking for a professional union, Butch, impressed by his shooting prowess and eventually renaming him the Sundance Kid, is able to convince him into that partnership for what each can do for the other, Butch to be the brains, and Sundance to be the shooting brawn. Despite wanting some notoriety both as an outlaw but also as an all 'round good guy who deserves some respect, Butch is trying to ween himself off criminal activities largely for the sake of his wife Mary and their two young sons, while Sundance is heading in the opposite direction wanting to commit as much lucrative crime as they can muster. In their somewhat opposing views, they agree to start with small robberies, ultimately, if possible, working their way up to more lucrative robberies, such as of trains. With various people after them for some of their past deeds, including one of Butch's former criminal associates, they will find through their criminal and non-criminal ventures if there is a future for them as partners.—Huggo