Steve Donegan, a politically ambitious prosecuting attorney, is framed for bribery by his nemesis, crime boss Joe Silenus. Steve is sentenced to prison where he again meets all the men he has convicted in his anti-crime crusade. Prison doctor Malcolm Scott warns Warden Parkhurst that Steve will be a marked man by his six thousand enemies, but the ineffectual warden refuses to offer Steve special protection. When an inmate tries to stab Steve, Anne Barry, a woman he convicted of embezzlement, saves his life by warning the guards with her screams. As Steve suffers the abuse of his fellow prisoners, his brother Phil begins to tail Silenus, determined to prove Steve's innocence. One day, while Steve is fixing a pipe in the prison laundry, he talks to Anne and, realizing that she too, was framed by Silenus, offers to help prove her innocence. After Steve is again brutally attacked by the inmates, Dr. Scott suggests that he can win their respect by meeting prison tough guy "Socks" Martin in the boxing ring. Steve is soundly beaten by Socks, but wins the convicts' admiration through his courage. Socks then warns Steve that he is marked for death and advises him to join a planned prison break. Soon afterwards, Phil is murdered by Silenus' men outside the prison gates as he is coming to visit his brother, and the gun shots trigger the prison break. Enraged by his brother's murder, Steve plans to escape, but after the convicts take Dr. Scott hostage, Anne convinces Steve to prevent the break by pumping steam into a passageway leading to the unguarded back gate. With the evidence that Phil uncovered, Steve is exonerated, and he returns to his post of district attorney to clear Anne and send Silenus to the electric chair.