In 1947, in La Santé Prison in Paris, the inmate Claude Gaspard is transferred to the cell of Geo Cassine, Roland Darbant, Manu Borelli and Vossellin a.k.a. Monseigneur. Gaspard befriends the four cell-mates that sooner disclose to him that they have long sentences and they have plotted an escape plan from the prison. Gaspard joins the quartet, digging a tunnel through the sewage system. One the day that they are ready to go, Gaspard is called to the warden's office and learns that his wife has dropped her accusation against him. He stays for two hours with the warden and when he returns to the cell, his mates have serious suspicions about what he had talked to the warden.
Source : IMDb