A mining camp during the California gold rush of 1849–50. The miners are drinking and playing cards at the Polka Bar when news comes via the Wells Fargo agent Ashby that a bandit named Ramerrez is operating in the area. He has a $5000 reward on his head. A quarrel breaks out between Sheriff Jack Rance and Sonora, one of the miners, over Minnie, the owner of the bar. It is only the arrival of Minnie herself that averts bloodshed. Minnie calms everyone down and leads a bible class.

Rance declares his love for Minnie, but she knows he’s married and rebuffs him. A stranger named Dick Johnson arrives; Minnie vaguely recognises him. They dance. Johnson – really Ramerrez – foregoes an opportunity afforded him to rob the bar: he and Minnie are falling in love. Later that evening, Minnie and Johnson are having dinner in Minnie’s cabin. A sudden snowfall forces Johnson to stay. As he goes to the bedroom, Rance bursts in, claiming Johnson is Ramerrez. Minnie gets Rance out of the cabin then confronts Johnson. He admits the truth and she orders him to leave. A shot rings out, and Johnson returns, injured. Minnie hides him in the loft. Rance comes looking for him. Johnson’s presence is betrayed by blood from his wounds dripping through the ceiling. Desperate, Minnie invites Rance to play poker: if he wins, he gets her and Johnson; if she wins, she and Johnson go free. Some sleight of hand saves the day. Rance is intent on revenge, and before too long the miners have caught Johnson and are about to lynch him. Minnie arrives and pleads for mercy. Her pleas prove futile until she threatens to shoot both herself and Johnson.

The miners relent and Minnie and Johnson ride off to a happier future.