Released for good behavior after five years in prison, Marcel Jacquin, a former robber, is welcomed by his granddaughter, Justine. His son, a police officer, has not shown him any sign of life since he was arrested. The grandfather will return to service, but this time, for a good cause, according to Justine. A medical student, a young man needs his grandfather's talents to break into the safe of a pharmaceutical laboratory that he suspects of culpable embezzlement. Justine wants to prove that t...