When Johnny Gray, a reckless, wealthy socialite, gets a speeding ticket, he is reprimanded by the father of his girl friend, Patricia Bedford, to reform his ways. While driving home from the Bedfords', Johnny's car is commandeered by four bank robbers led by Rico. The police follow Johnny because of his reckless driving but when he pulls into a side street, Rico escapes with the money, promising his partners that he will meet them later. The police apprehend Johnny and the robbers, who then implicate Johnny as their crime boss in order to keep Rico free. Headlines dub Johnny the "thrill bandit," as his wealth precludes his having stolen for the money. Johnny and the robbers are convicted and sentenced to ten years in San Quentin Penitentiary. Johnny becomes an embittered and hostile inmate and befriends Cain, the prison's most hardened criminal. Bent on revenge against the men who framed him, Johnny picks a fight with Creeper, one of the robbers, and is placed in solitary confinement for a month. After Johnny is released from solitary, Cain is impressed by his fortitude and includes him in his escape plan. Some time later, when the brutal warden is dismissed because of a prisoner's suspicious death, the governor replaces him with former prison guard Frank Sanders, an idealist who plans to reform the prisoners. Cain and Johnny hope to take advantage of Frank's leniency to aid their escape. Frank asks Johnny's help in rallying the prisoners to take part in his athletics program, but Johnny refuses. Frustrated, Frank seeks advice from his friend, Amy Duncan, who has received professional training in juvenile delinquency and is the head guard's daughter. Frank follows Amy's advice and puts Cain and Johnny into separate cells to keep them apart. Believing that Johnny can be reformed, but Cain is hopeless, Frank puts Johnny to work outside planting petunias. Amy is delighted when she meets Johnny outside her house, as he once was her college hero, however, Johnny remains surly. Amy nevertheless sees his innate goodness when Johnny moves a flowering plant from her house to outside a prison wall so that Wayne, an inmate about to be executed, can see a flower before he dies. Soon Creeper and his cohorts attempt to escape and are shot to death as they climb the prison fence, but before he dies, Creeper tells Frank that Johnny is innocent. Johnny then receives a full pardon and truly intends to leave the prison, as Patricia waits for him outside, but after he gives Amy a farewell kiss, he decides to accept Frank's job offer to work as a prison guard. Cain mistakenly believes that Johnny is still on his side, and agrees to rally the men to play baseball to help Johnny impress Frank. Johnny avoids Amy because he thinks Frank is her boyfriend, but Frank assures him that their friendship is platonic. When Johnny refuses to aid Cain's escape, Cain takes him and Duncan hostage, and after freeing the prisoners from their cells, incites them to riot. The governor allows Frank half an hour before he sends in the troops, and Frank announces to the prisoners that he will end all his reforms if the prisoners do not return to their cells. Johnny also attempts to talk to the prisoners, and when Cain strikes Johnny and a prisoner comes to Johnny's aid, Cain shoots the prisoner. The rest of the prisoners converge on Cain, and Frank quells the riot. Finally free, Johnny goes to Amy.