Paul Delorme, secret agent, is about to go on vacation. But he is summoned by his superiors, an undercover agent has just been hit by a car in Amsterdam. Murder or a trivial car accident? Delorme will have to investigate.
Paul discovers the corpse of the American tourist at Lydia's, and the police get involved. Lydia's fiance, William Danjou, is suspicious. On his way home, Paul discovers two armed men.
Paul continues the investigation and is revealed to him the existence of a diamond trafficking in which the killed spy was possibly involved. Lydia continues to assure the police that she does not know anything and approaches the agent.
After going to the underground diamond dealer, Delorme is in an uncomfortable situation, it seems that his coverage is compromised. During the night, events take him on new tracks.
The investigation progresses and Paul and Lydia get closer, but for what reasons? L'Héritier, the police officer in charge of the investigation, thinks of finding new leads and in particular, a new suspect.
