The warden of the notorious Sing Sing penitentiary stakes his reputation, career and the future of the prison's inmates on the honor of a thief and murderer--betting that the man will return voluntarily to face his execution at the federal penitentiary known as the Castle on the Hudson. When hardened thief Tommy Gordon is sentenced to serve a prison term at Sing Sing, he believes his friends will help him get out. But after some time the incorrigible prisoner realizes that his associates on the outside are not going to help him, and under the guidance of reformist warden Walter Long, Gordon gradually becomes a model prisoner. When Gordon's girlfriend, Kay Manners is attacked, Long grants Gordon a furlough to see her. But Gordon confronts her attacker and kills him. Now, Gordon can choose to flee with Kay..or return to prison-saving the work of the only man who has ever believed in him and to a one-way walk to electric chair.