The minimal plot involves two women whose personalities are in sharp contrast when they first meet and move in together. The third woman of the titular three is a key supporting character—a mural artist (Rule) who owns, with her husband, the same apartment building. The events take place in a small desert community typical of those found east of Los Angeles. For obvious reasons the film has a dream-like quality, focusing more on behavior, mood and mystery than on plot devices.
What the film is about exactly is open to interpretation, and even Altman said he was not sure what the ending means but has a "theory" about what happens. What is clear is that the two principal characters undergo a transformation in which they exchange their relative status to each other. In this way, 3 Women has a kinship with Bergman's Persona (1966).
Duvall plays Mildred "Millie" Lammoreaux, a woman who is very confident of her personal charisma, and her attractiveness to men in particular, despite the fact that the men she hits on openly mock her. In the director's commentary on the Criterion edition, Altman claims that Duvall was responsible for creating her character's diary entries, recipes, and much of her dialog in the film. Spacek plays Pinky Rose, a naive, childlike woman, who refuses to talk about her past and who initially idolizes Duvall, but eventually comes to dominate her. They both work at a physical therapy facility and much of the film takes place at their apartment building, where the third woman, Willie Hart, played by Janice Rule, creates striking and somewhat unsettling murals (actually painted by the artist Bodhi Wind).