Nounours is the slang name for a "cousin," also known as an informant who has a specific deal with the authorities whereby he receives 10% of the drugs that are recovered as a result of his assistance. Inspector Gérard Delvaux takes over the investigation after his personal contact, Inspector Maurin, takes his own life. In the meantime, Judge Lambert is conducting an investigation into the unlawful behavior of the police officers. Her dogged investigations, which had previously cornered Maurin, are now heading to Gérard, and also to Nounours, as the source of the heroin that led to the latest instances of fatal overdoses. Before he is compelled to divulge who Nounours is to judge Lambert, Gérard is determined to realize Nounours' promises of increasingly larger catches. Nounours makes these promises to Gérard.