An army officer is hired to discipline prisoners but falls in love with the sister of an inmate who tries to escape.
In prison acting captain Druggin (Barton MacLane) gives inmates extra punishment; but Warden Taylor (Joe King) demotes him to try army officer Steve Jameson (Pat O'Brien). Steve hears Mae Kennedy (Ann Sheridan) sing "How Could You?" and meets her. Red Kennedy (Humphrey Bogart) asks Mae for money; but he is caught by police after shooting at them. Steve learns that Red is Mae's brother. Steve meets the inmates, who are called boys, and he makes one sing. Joe is brought in and meets Steve, who suggests he learn a trade. Hanson (Joe Sawyer) fools Red into believing he is pardoned. When they laugh at him, Red socks Hanson. Druggin recommends a month of solitary, but Steve gives him four days.
Steve goes to see Mae, who cooks dinner for him and complains she could not see Red, because he lost his privileges for a month. Mae visits Red and gives him money, but she is caught. Druggin takes her to Steve, who tries to explain. Steve suspends Red's privileges for a month again. During inspection Steve converses with several inmates. Hanson works next to Red and suggests the road gang for escaping. The religious fanatic Rogers (Garry Owen) is mocked. A guard drops a rifle; Rogers picks it up and shoots a guard. Steve talks to Rogers and gets the rifle. Red gets the road gang sooner than others. Men decide to strike because of it and sit down in the yard. Steve asks them why and says no chow until they obey. Men go back to their cells but shout. Druggin tells a reporter, and the board changes Steve's work orders. Steve says those who can be reformed should be given privileges but not the habitual criminals. Mae arrives to see Steve and thanks him.
Hanson tells his girlfriend Helen (Veda Ann Borg) where to come near the road gang. Druggin learns that Hanson talked of escape. Red likes working on the road and does not want to help Hanson escape until he learns that Steve favors him because of his sister. Helen lets the air out of a tire and drives by the gang. Hanson and Red change the tire and get guns. Red knocks out a guard, and Hanson takes Druggin in the car. Hanson hits Druggin and throws him from the speeding car. Police shoot the gas tank. Hanson and Red take another car and smash through a road block, but a train causes them to crash. Steve learns that Druggin and Hanson are dead. Red buys bullets. Steve calls on Mae. Red comes in and shoots Steve, but Mae helps Steve capture Red. Police arrive, but Steve denies the shots while Red escapes. Police shoot at Red, who gets a ride. Wounded Red goes back to San Quentin and says that Steve is good as he dies.
Mean treatment by Druggin is replaced by a more intelligent approach by Steve though his denying privileges to "habitual criminals" is suspect. The drama is melodramatic, but Red learns that Steve was trying to help him.