Warden Clinton T. Duffy of San Quentin penitentiary introduces three short stories about prison life: Prisoner Billy Brenner, a gourmet, is dismayed to discover that Louis, the prison's head chef, is about to be paroled and offers him two hundred dollars a week to stay. However, Louis leaves and obtains a position as chef at a high-class restaurant where his girl friend Marie also works. One evening, a very particular customer visits the restaurant and Louis suggests a special dinner. When the customer is not totally pleased with the first course, Louis, who has a problem controlling his temper, manages to remain calm. After another course is rejected, Louis presents his coq-au-vin specialty whereupon the customer brings out a bottle of ketchup and slathers it over the dish. This enrages Louis, who then smashes a plate over the customer's head, thereby breaking not only the plate, but also the conditions of his parole. After Louis is returned to the prison, his assistant Solly tells him that a week before the incident in the restaurant occurred, he had heard that Louis would be coming back. Louis realizes that he has been framed by Brenner and his pals and deliberately prepares inedible meals for them. Meanwhile, Mrs. Duffy discovers that the restaurant customer was an ex-con and confidence man named Gilbert Lee, alias "Phil the Hook," and tells her husband. Fed up with the poor food, a number of the convicts tell Louis that Brenner planned the whole thing. Louis then threatens Brenner with a meat cleaver and forces him to eat rice pudding covered with ketchup. Later, after Duffy informs Louis that his parole has been reinstated, he hands his chef's hat to Solly and leaves to meet Marie, as Lee joins the prisoners' ranks.Warden Duffy's second story concerns an attempted prison break from an isolation area: One night, prisoner Chet Harmon feigns illness and Frank, a male orderly and prisoner, is summoned. Frank's brother Al, who is in an adjacent cell, tells Frank that he and Chet are planning a breakout and that he has to help. Frank is reluctant to assist as he just wants to serve his time and leave, but after a new prisoner sows doubts in Frank's mind about his girl friend's faithfulness, he decides to help. Later, while the prison doctor is examining Chet, Frank removes a gun from the doctor's medical bag and slips it into an unoccupied cell. When Frank is on his way out, he attacks a guard named Pete and is put in the cell where he placed the gun. With Al's help, Frank passes the gun to Chet. Another prisoner, Square, is also in on the escape. Three days later, when two members of the prison board, Garvey and Ferness, visit the cells on a routine inspection, Chet uses the gun to take Garvey and Pete prisoner and locks them in a cell. Chet then releases Al, Square and Frank and, using Ferness as a hostage, phones Duffy to demand that a car be delivered to the gate and that they be given a two-hour head start. When Duffy refuses to cooperate, Chet tells the warden that in ten minutes' time he will begin to kill the hostages. Frank wants nothing to do with killing, but while he and Al discuss this, Chet kills Pete and sends his body to Duffy. After Duffy reports to his chief, Square arranges that Duffy come, under a truce, to negotiate. Duffy tells Chet that his chief will be coming within two hours to make a deal. However, Chet then attempts to add Duffy to the hostages, prompting Square, who had given Duffy his word regarding the truce, to tackle Chet. Frank helps but is shot and seriously wounded by Chet, who then kills Square. Duffy says that Frank will die, but refuses to summon the doctor until they abandon the break. When Al, desperate to help his brother, goes to the phone to call the doctor, Chet threatens to shoot him, but Al draws a knife. Chet shoots him, but Al sinks the knife into Chet and they both die.Duffy's final story is about a prisoner's need to find a purpose in life: When Duffy shows new prison chaplain Father Harvey around the chapel, the priest is saddened to see that a mural of "The Last Supper" has been damaged by rusty water pipes. After Shorty, a convict who is to assist Harvey, tells him that a prisoner named Steinberg, who is serving a life sentence for murdering his wife and her lover, is a very fine artist, Harvey persuades Steinberg to repair the mural. Access to the chapel is important to Shorty and his pal Mike as they plan to make bootleg liquor in an attic they can reach only from the chapel. Steinberg agrees to assist their project in return for a cut of the sales. Steinberg, who is an atheist and resents the priest's artistic supervision of his work, begins the restoration work with the face of Simon Peter. When Harvey discovers that the face Steinberg has given Simon Peter is that of a prisoner who was executed on the eve of Harvey's arrival, the priest accuses Steinberg of mocking religion and demands that he be disciplined and lose certain privileges for a week. Later, Steinberg discovers that Shorty and Mike are really planning a breakout via the attic and may take Harvey as a hostage. Steinberg resumes his work and finishes the face of Matthew. Meanwhile, Harvey is concerned about how he will deal with an imminent execution, and when he goes to Charlie Rivers' cell to hear his final confession, he realizes that Steinberg has given Matthew the condemned man's face. After Rivers tells Harvey that he is innocent and begs him to intervene, the priest talks with Duffy, who regrets that he is powerless and states that the horrible thing about capital punishment is that you never can be sure about guilt and innocence. This increases Harvey's anguish and, although he agrees to accompany Rivers to the execution chamber, he collapses on the way. Rivers then tells the priest that he is really guilty and seeks his help on his final journey. That night, Harvey tells Steinberg how Rivers helped him and admits that he has been prejudicial. Later, Shorty, who has become the model for the mural's Judas, Mike and Steinberg take Harvey hostage at gunpoint and attempt to break out. After Mike is killed by guards, Shorty has Harvey phone Duffy to arrange their release, but Duffy tells him that the guards have orders to shoot, regardless of who the hostage may be. Steinberg then tackles Shorty, refusing to permit the possible killing of the priest. Although Shorty mortally wounds him, they continue to struggle until Shorty falls on top of Steinberg and the gun goes off, killing Shorty. Father Harvey prays over Steinberg's body. Later, Harvey engages another artist to finish the mural, with the face of Christ to be Steinberg's.