The title refers to the belief that Billy the Kid was left handed, and he shoots left-handed in the film, though this was a false conclusion drawn from a reversed photograph.

The film attempts to portray Billy the Kid as a misunderstood youth who got mixed up in a cattle war and was dragged down by the hostile population of New Mexico.

Drifter William Bonney, known as "Billy the Kid", befriends a cattle boss named John Tunstall, who is known as "The Englishman".

Tunstall is murdered by corrupt rival cattlemen led by the local sheriff in the Lincoln County War.

In a final showdown, Garrett ambushes and kills the exhausted Bonney, who faces his nemesis unarmed in the hopes of ending his own life.