At a beach house one night, we see a man, Monte Beragon, getting shot, and his last dying words are, “Mildred.”
We then see Mildred Pierce Beragon contemplating suicide, but she is talked out of it by a cop nearby. She goes into a nearby nightclub, run by her old business associate, Wally. After a drink, Mildred convinces Wally to come back to the beach house with her and they have a drink. Wally has long been romantically interested in Mildred, but she has never taken the bait. Tonight she leads him on more, but when she flees the house and locks him inside with the dead body of Monte Beragon, we realize it was all a setup.
After Wally gets framed for the murder of Beragon, Mildred is apprehended by the police and brought in for questioning by an Inspector Peterson. In his office, he tells Mildred that he thinks the crime was committed by Mildred's ex-husband, Bert Pierce, but Mildred insists this isn't the case, and begins to tell her story.
In flashback, we see Mildred living in a house in Glendale, California with Bert and their two daughters, Veda and Kay. Bert, who was in the real estate business with Wally, loses his job because of the Depression and Mildred begins baking pies for neighbors and friends to earn a little extra money. Bert disapproves of the way Mildred fawns over their older daughter, Veda, and feels humiliated by the fact that Mildred has taken a job. As a result, he has begun an affair with Maggie Biederhof, and when he gets a call at home from Maggie, Mildred kicks him out once and for all.
Left to provide for her children on her own, Mildred takes a job as a waitress at a restaurant. She soon ascends the ranks, becoming the best waitress there. She goes to Wally and asks him to help her open her own restaurant, and they scope out an abandoned building owned by a wealthy society man named Monte Beragon. Beragon is reluctant to sell to Mildred at first, but when they promise to make the business thrive, he agrees.
Mildred's restaurant takes off, and she is soon a successful businesswoman. Not only that, but Monte Beragon seduces her soon enough and the two begin an affair. However, on the first night that Mildred goes over to Monte's for a night alone, her younger daughter Kay falls ill with pneumonia and dies. Haunted by the tragedy of her daughter, Mildred throws herself into her work, opening up a chain of restaurants that continue to thrive. While things seem stable and happy, her older daughter, Veda, is spoiled and is not satisfied with what her mother has to give her.
As her mother becomes more successful, Veda begins courting a wealthy boy named Ted Forrester, with whom she elopes. Ted's mother does not approve of the marriage, but when they try to settle the case out of court, Veda says she's pregnant, demanding money for her trouble. When they return home, Mildred learns that Veda lied about being pregnant just to earn some extra money and angrily throws Veda out of her house.
After a brief time traveling, Mildred returns home to Glendale, and Bert takes her to Wally's nightclub, where Veda is performing. Mildred is heartbroken to see her daughter forced to be working in a nightclub, and offers for Veda to come live at home. Veda, true to form, insults Mildred lifestyle and tells her she can never provide the kind of life she wants.
Determined to get Veda back, Mildred buys Monte's home in Pasadena and proposes marriage to him, even though she doesn't love him. He agrees, on the condition that she give him a one-third share in her restaurant. She soon realizes that Monte is overspending and driving her business into the ground. After a meeting with some lawyers and business associates, Mildred drives to Monte's beach house to confront him, but when she arrives there, she finds him having a tryst with Veda. Veda gloats to her mother that Monte plans to marry her and that they have been having an affair for a while. Mildred leaves the beach house, enraged and defeated.
After Mildred leaves, Monte tells Veda that he has no intention to marry her, and she becomes so angry that she shoots him multiple times. Veda is the killer, and Mildred comes back into the house when she hears the gunshots. While at first she resolves not to help Veda get out of the mess she's in, Veda soon convinces her to help her and save her from getting arrested. When the scene shifts out of the flashback, Inspector Peterson informs Mildred that he knew that Veda was the killer all along. Veda is arrested, and Mildred leaves with Bert.
