It's 1989 and Josey Aimes (CHARLIZE THERON) is simply looking for a better life for herself and her kids, teenager Sammy (THOMAS CURTIS) and his younger sister Karen (ELLE PETERSON), following one too many beatings from her abusive husband. Unfortunately, her traditional parents Hank (RICHARD JENKINS) and Alice (SISSY SPACEK) blame her for her marital woes, leading her to leaving her kids with her best friend Glory (FRANCES McDORMAND) and her husband Kyle (SEAN BEAN).
Having never supported herself let alone her family, Josey needs a high-paying job and the only such game in town is working for Pearson Tacomite and Steel, a northern Minnesota mine. Glory works there -- as a union rep. -- and so does Hank, but neither they nor Kyle are sure she's suited for the work. Nevertheless, she takes the blue collar job, working alongside a handful of other women such as Big Betty (RUSTY SCHWIMMER) and teenager Sherry (MICHELLE MONAGHAN).
It's not long, however, before Josey learns why few women work there. The men, not used to women working alongside them -- especially ones as pretty as her -- immediately objectify her, taunting her with all sorts of sexual comments and come-ons. That includes her immediate supervisor Bobby Sharp (JEREMY RENNER), her former high school classmate and romantic interest who's turned into a chauvinistic, callous man.
Despite Glory telling Josey she needs a thicker skin, all of the sexual harassment -- combined with the lack of concern on the part of the male-dominated chain of command above her -- eventually becomes too much to bear. Pressured to quit, she hopes to enlist the aide of Glory and Kyle's friend Bill White (WOODY HARRELSON) who's just arrived there from New York City in hopes of regrouping his life. Having given up his law practice, he wants nothing to do with Josey's efforts, but she eventually wins him over.
From that point on, and with Bill's help, she must contend with the reaction of her family, friends and former coworkers as she files a class action, sexual harassment claim against the company and its boss, Don Pearson (JAMES CADA), who does everything in his power to discredit her claim and personal life.