It is California , during the years of gold-rush fever,1849-1850. Minnie runs a bar for the miners, mothering them, and caring for their spiritual welfare. Sheriff Jack Rance is in love with Minnie, but his affections are not returned. The miners are gathered playing cards when Ashby, the Wells Fargo Agent, arrives and tells Rance that he is following the trail of a notorious bandit, Ramerrez. A stranger, Dick Johnson (Ramerrez in disguise) enters, looking for a drink. He and Minnie recognize each other from having met many years before, and much to the Sheriff’s annoyance, she and the stranger dance together. The capture of one of Ramerrez’s accomplices is announced, and the robber is dragged into the bar. Recognizing Johnson/Ramerrez, he bluffs that he can lead the men to the bandit’s hideout and they all depart, leaving Minnie and Johnson alone. Learning that she alone guards the miners’ treasure of gold with her life, he abandons his original plan to rob the saloon and accepts Minnie’s invitation to her cabin for dinner.
Act II: Minnie tells Johnson of her exciting life in the mountains, and they declare their love for each other. They are interrupted by banging on the door: it is Sheriff Rance with some of his men. Minnie quickly hides Johnson, and the Sheriff enters to tell her that he has discovered that the stranger, Dick Johnson, is really Ramerrez in disguise. Minnie sends them away and becomes furious with Johnson for deceiving her. Even although there is a blizzard raging outside, Minnie sends him out into the night. No sooner has he left than a shot rings out: the Sheriff, seeing Johnson leaving the cabin, has wounded him. Minnie, overcome by love, helps Johnson back inside and hides him upstairs in the attic. Sheriff Rance returns and demands Johnson/Ramerrez. He is just about to leave, having been convinced by Minnie that Johnson is not there, when a drop of blood falls from the loft onto his hand. In desperation, Minnie strikes a bargain with the sherrif: they are to play a hand of poker, and if she loses, she will become Rance’s and Johnson will be brought to justice. However, if she wins, Johnson will be allowed to go free. Minnie wins by cheating and Rance leaves, furious at having lost the bet.
Act III: After recovering from his wound under Minnie’s care, Johnson leaves her and is captured by the miners, who plan to hang him. Pleading with them to tell Minnie nothing of his fate, only that he found a new life far away, Johnson asks them to finish the job quickly. Minnie arrives at the last moment and begs for Johnson’s life, reminding the miners of all she has done for them, and saying that the greatest teaching of love is that the worst sinner can be redeemed. Despite Rance’s jealous protests, Johnson is freed by the crowd and he and Minnie leave to find a new life together.