Four cellmates who expect long prison sentences, or execution by guillotine, are determined to escape. Before they can start digging a tunnel, the prison staff puts a man arrested for attempted first-degree murder, Gaspard, into their cell. They have no choice but to fill him in. At first he is enthusiastic about taking part in the getaway, but as the tunnel nears completion the warden tells him that his alleged victim has withdrawn the charges and that he will be released soon. Returning to the cell, Gaspard has to dispel the suspicions of his cellmates that he turned them in. He does, and they continue with the escape as planned. However, in the last moments, before the five are just about to leave through their tunnel, they understand that they have been betrayed. The last scene is of the four cons being stripped to their underwear before going into solitary confinement, and of Gaspard, walking to his cell down the hall, clothed in his escapee street clothes, where he will await discharge.