Among the new arrivals at the Women's State Prison is nineteen-year-old Marie Allen, who has been sentenced as an accessory in a gas station robbery during which her husband was killed. Marie's physical examination reveals that she is pregnant, and so Ruth Benton, the warden, assigns her to work as a checker in the laundry. When Evelyn Harper, the matron of Marie's cell block, who exchanges favors for money, learns that Marie has no money, she reassigns her to cleaning the cells. Marie is befriended by toughened convicts Smoochie, Kitty Stark and Claire, who reveal that, like Marie, most of the women are in prison because of men. As her pregnancy advances, Marie becomes ill. Although she will still be in jail when the baby is born, Marie hopes that her mother and stepfather will care for the child until she is paroled. Kitty suggests that Marie join her shoplifting racket when she gets out, explaining that even if she is paroled, she will be forced to stay in jail until she is offered a job. Marie, however, turns the offer down. One of the convicts then has a psychotic breakdown, and when June, another convict, is denied parole, she hangs herself. After Marie goes into early labor, the volunteer doctor expresses his disgust at prison conditions, and Benton makes a proposal to the medical board that her budget be increased. Benton is aware of Harper's sadistic treatment of the women, but her efforts to have the matron fired are always stymied by Harper's political friends. Similarly, her demands for teachers and a psychologist are denied by the prison board. After Marie's mother refuses to take her baby, he is put up for adoption, and as Marie's parole hearing nears, Kitty renews her job offer. Despite Benton's favorable recommendation, Marie's parole is denied. Meanwhile, Elvira Powell, an enemy of Kitty's, is sent to prison. Her wealth easily buys Harper's favoritism, and she is made comfortable. Elvira tries to befriend Marie and recruit her for a call girl ring, but Marie remains loyal to Kitty. One day, while Kitty tries to train a convict in shoplifting techniques, a more hardened Marie demonstrates how easy it is to fool a spotter. Elvira then suggests that Harper inform Benton that Kitty is recruiting women for her shoplifting ring. Kitty is placed in solitary confinement and beaten. After Marie finds a lost kitten, Harper's efforts to remove it lead to a riot. As punishment, Benton rescinds all privileges for the woman and sentences Marie to solitary confinement. Without Benton's knowledge, Harper shaves Marie's head, and Benton again tries to have Harper removed from her position. Harper's friends see that her efforts backfire, and Benton is asked to resign. After Marie returns from the hospital, Kitty kills Harper with a fork. Determined to leave prison at any cost, Marie asks Elvira for help and obtains parole. Despite her efforts, Benton has been unable to reform her prisoners, and after Marie leaves, instructs her secretary to keep her file active, because "she'll be back."