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 the laboratory is testing, completely illegally, an experimental vaccine on the civilian populations of an African state at war. The evidence is kept in the safe, and whoever says forced safe necessarily says Marcel..