Calamity Jane is a tough and rowdy woman in the old West who owns a saloon and gambling joint (and runs a cattle rustling operation as a sideline). One day she hires a pretty but naive young woman to work as a saloon girl, and finds that the girl is bringing out the maternal instincts she never knew she had. Those instincts are put to the test when a US army cavalry troop arrives to clean up the town and the girl and the young lieutenant in charge of the troop fall in love, and Calamity Jane may know something about the lieutenant that the girl doesn't.