Inspector Maigret investigates the mysterious murder of a Dutch diamond dealer, found dead in a stolen car. The car belongs to an insurance agent, Michonnet, and has been abandoned in the garage belonging to Carl Andersen.

Sisif, a railwayman, saves a young girl named Norma orphaned by a train crash and raises her as his own daughter alongside his son, Elie. As she becomes an adult, Sisif grapples with whether to tell Norma the truth about her parentage.