First time criminal offender, housewife Helene Jensen, and forger Brenda Martin check into a maximum security prison, which houses both men and women, separated only by cement walls and numerous guards. Helene, convicted of manslaughter for killing a child in a car accident, shrinks in terror at her harsh surroundings, while Brenda, who has broken parole, reunites with several of her prison friends. Convicted thief Glen Burton, part of a men's paint detail working near the women's wing, attempts to find his prisoner wife Joan, but, after a brief scuffle, is taken to Warden Brock by police captain Tierney. Brock refuses to allow Glen to see Joan and sentences him to twenty days in solitary. Prison physician Dr. "Doc" Clark is displeased with Brock's treatment, but refrains from making any comments. Matron Sturgess then summons Doc to the women's wing to examine Helene, who remains tense and fearful. After administering a mild sedative to Helene, Doc advises the women's prison director, Amelia Van Zant, to forego the usual month-long isolation of new prisoners with the sensitive Helene, but Amelia disregards his suggestion. When Helene is placed in a darkened solitary cell, she grows terrified of the loud, unexpected prison noises and becomes hysterical. Amelia orders Helene placed in a straitjacket and a padded cell, where her shrieks go unheard. The following morning, an alarmed Sturgess finds Helene unconscious and summons Doc who, despite Amelia's protests, orders Helene placed in the infirmary. After Helene revives, Doc calms her by promising to smuggle in letters from her husband. Two weeks later, a recovered Helene is placed with the other prisoners and Brenda takes her under her wing. When Helene's husband Don visits after the requisite waiting period, he offers her encouragement by telling her that he has hired another lawyer for an appeal, but Helene inadvertently cuts short their visit and is taken away when she touches the screen between them. Outraged, Don insists upon seeing Amelia, but she remains coolly evasive. Doc learns that Amelia has ordered Helene placed in solitary and objects strenuously, to no avail. Meanwhile, Joan grows concerned upon learning from a recently paroled inmate that Glen intends to see her somehow. Soon after, while the women toil in the prison laundry facility, Joan discovers Glen hiding in a small storage room. He reveals where the money he stole is hidden and asks Joan to contact a friend of his to use the money to get him out of prison. Brenda accidentally stumbles upon Glen and Joan and a little later, intentionally burns herself on one of the steam machines to prevent matron Enright from discovering the couple in the storage room. A few days later, Doc's attempt to get Helene out of solitary fails when Amelia interferes, claiming she is only following prison regulations. One day while working in the laundry, Joan faints and later she confides in Brenda that she is pregnant. Doc reports Joan's pregnancy to Brock and Amelia, and the warden immediately summons Glen. Doc advises that they parole Joan immediately, but Brock rejects the suggestion. When Glen arrives, Brock demands to know how he visited his wife, but Glen declares that only when Joan is paroled will he confess. Frustrated, Brock demands that Amelia find out the truth from Joan in one week or he will fire her. Amelia cancels all prisoner visiting and letter writing privileges and over the next few days harasses Joan in an attempt to force her to talk. As the week nears its end, Amelia gets frantic and one evening, after ordering the guards out of the interrogation room, beats Joan, whose screams arouse the other prisoners. Doc takes Joan to the infirmary and furiously informs Amelia that Joan may not survive. The next morning the women prisoners refuse to eat or work in protest of Amelia's treatment of Joan. Doc reports to the warden that Joan is hanging on, but that should she die he intends to accuse both Brock and Amelia of murder. That night several women prisoners stage a rebellion, using knives as weapons. At the same time, having heard of Joan's condition, Glen sneaks back into the women's wing to see her. Using her talent for mimicry, one of the prisoners, Dottie, imitates Sturgess, allowing the women to get into Amelia's office and take her prisoner. Meanwhile, Glen gets to the infirmary to speak with Joan before she dies. Outside the infirmary, Doc learns of the uprising and tells Brenda of Joan's death, which outrages the women. Doc cautions the prisoners that if they harm Amelia they will ruin their parole chances and the opportunity to change the prison system. Having discovered Glen's absence from the men's block, Brock orders a search. Armed guards fire gas canisters into the women's wing, breaking up their revolt and hampering the bereft Glen, who, armed, stalks Amelia. Amelia escapes from the women in the confusion of the gas, but Glen follows, cornering her in the padded cell. At the last moment, Doc prevents Glen from shooting Amelia, who, under the terror and pressure, mentally collapses. The following day Brock confidently tells Doc he believes the worst is over, but Doc assures him that once the full truth is known, his days as prison warden will be numbered. Soon after, Helene is paroled and reunited with Don.