Father Charles Dismas Clark, a Jesuit priest in St. Louis, dedicates his life to the rehabilitation of delinquents and ex-convicts. By meeting them on their own terms and talking their language, he wins their confidence and their trust. He is primarily concerned with a young thief, Billy Lee Jackson, recently released from the Missouri State Penitentiary. Father Clark helps clear the boy of some trumped-up charges and then gets him an honest job with a produce market. Billy's rehabilitation is further encouraged by Ellen Henley, a young socialite with whom he falls in love. Meanwhile, aided by Louis Rosen, a successful criminal lawyer, Father Clark raises enough funds to open Halfway House, a shelter for ex-convicts readjusting to civilian life. All goes well until Billy's employer fires him for a theft he did not commit. Embittered, he and a friend, Pio, attempt to rob the produce market. They are caught by one of the owners, and he attacks Billy with a crowbar. The panic-stricken boy grabs a gun and kills him. The police chase Billy to an abandoned house, and he hides there until Father Clark persuades him to surrender. Tried and convicted of murder, he is sentenced to death. Before Billy dies in the gas chamber, Father Clark reassures him by telling him of Penitent thief, the thief who died on the cross, and of how Christ promised him eternal life. After the execution, Father Clark returns to Halfway House and finds his first client, Pio, drunk and repentant.