Four prison inmates have been hatching a plan to literally dig out of jail when another prisoner, Claude Gaspard, is moved into their cell. They take a risk and share their plan with the newcomer. Over the course of three days, the prisoners and friends break through the concrete floor using a bed post and begin to make their way through the sewer system - yet their escape is anything but assured.

Michel Constantinas Geo Cassine
Jean Keraudyas Roland Darban
Philippe Leroyas Manu Borelli
Raymond Meunieras Vossellin / Monseigneur
Marc Michelas Claude Gaspard
Jean-Paul Coquelinas Le lieutenant Grinval
Eddy Rasimias Bouboule
Philippe Dumatas Un gardien
Albert Augieras Un gardien