Nounours is the nickname of a "cousin" an informer with a special arrangement with the police: he gets 10% of the drugs seized thanks to his help. When his personal contact, inspector Maurin, commits suicide, inspector Gérard Delvaux takes over. Meanwhile, judge Lambert is uncovering the illegal practices of the policemen. Her persistent investigations, which had cornered Maurin, are leading to Gérard, and also to Nounours as the source of heroin that led to recent cases of deadly overdoses. Nounours promises Gérard increasingly bigger catches which he is intent on realising before he is forced to reveal who Nounours is to judge Lambert.