Four convicts in a French prison share a single cell. As all are incarcerated for serious crimes, including, perhaps, execution, they decide to escape and have collected materials for the purpose. Before they can begin carrying out their carefully prepared plan, another inmate is moved to their cell. What now? They have no choice but to tell him what they intend to do. He becomes an accomplice, and all five begin the laborious and very clever process of digging their way through the concrete floor to access underground tunnels beneath the prison and, eventually, the sewers to which those tunnels are connected.After much work, they find a way out onto the streets of the city, not far from the prison. But they must wait until the next night to effect their escape. During their final day, the newcomer is taken to the warden, who informs him that the charge against him has been dropped and that he will be released very soon, though not on that day. After a two-hour meeting, he is returned to the cell, where he is questioned, his faithfulness to the plot is challenged, he is accused of ratting on his mates, and he finally wins back their trust and gains an apology. What has he done? Can the plot succeed?