Racketeer and political boss Johnny Moon cold-bloodedly kills one of his lackeys and is later found innocent of the crime. Johnny's sister-in-law, schoolteacher and trained psychologist Helen Martin, is then dismissed from her job because the school board fears that she will be a bad influence on the children. Although Helen's sympathetic supervisor, Dalvers, recommends her for a job teaching at the women's County Corrections School, Helen decides to leave town and urges her sister Jean to accompany her. Jean, however, is committed to unfaithful Johnny, and refuses to leave. Helen reconsiders her departure and applies for the reformatory position, after which she is questioned by policeman Frank Donovan, an inspector for the county board. Although the conservative women who head the board oppose Helen's employment because of her connection to Johnny, Frank wholeheartedly recommends her, and convinces the other board members, Reverend Greene and Lionel Cleeter, to vote in her favor. One of the inmates dies due to neglect on the same day that Helen reports for duty, and Helen is appalled by the poor conditions at the reformatory. However, Marcus, her supervisor, keeps a tight rein on her activities. Helen tries to be a positive and encouraging force for the jaded women who populate the reformatory, but Marcus and his helper, Mrs. Peters, thwart her attempts at every opportunity. Johnny's most recent girl friend, Rita, a waitress, is installed in the facility, but Johnny ensures that she gets special treatment. One day, the women riot and are put in solitary confinement. Helen confronts Johnny and vows to report the wretched conditions to the governor if Johnny does not make improvements. Johnny then reprimands Marcus for chiseling money from the reformatory and advises him to lay off of Helen. Helen, in the meantime, has combined her efforts with Frank to get proof that Mayor McCarthy is corrupt and takes orders from Johnny. As part of their plan, Frank and Helen bring Rita's former boyfriend, Tom Havershield, to visit her. Touched by Tom's concern, Rita undergoes a reformation and promises to testify against Johnny. Johnny forestalls this by releasing Rita from prison and murdering her, and he has Helen suspended from her job. Frank relentlessly pursues the murder investigation, but comes up with nothing. Cleeter, who has become a hapless drunk and witnessed Rita's murder, confronts Johnny, who throws him off the edge of a newly constructed dam. Cleeter clings to life and calls Frank to his hospital bed to tell him he is a witness. Helen warns her sister that Johnny is about to be arrested, but Jean refuses to leave, and the apartment is surrounded by police. Frank follows Johnny onto a rooftop and is forced to kill him in self-defense. Later, with Helen and Frank's evidence, the governor dismisses McCarthy after revealing his corruption, and appoints Helen as the new corrections facility superintendent.