Series One takes place in the 1930s with Commissaire (approximately DCI) Larosière (Antoine Duléry) and Inspecteur Lampion (Marius Colucci).

[5] Set in northern France in the 1930s, womanising and bombastic Commissaire Jean Larosière and his hapless junior officer Inspecteur Émile Lampion unravel a series of complicated murder cases to reveal the killers.

Suave, razor-sharp, arrogant, and intolerant – Commissaire Swan Laurence investigates murders with the often unappreciated assistance of reporter Alice Avril and police secretary Marlène Leroy.

After a night of drunken revelry that she cannot recall, Avril awakens in bed next to the corpse of young man with a knife in his chest.

Laurence has resigned as Commissaire and is about to leave for Washington to work for the FBI but, joined by Marlène, Glissant, and Tricard, he goes to extraordinary lengths, including illegalities, to figure out who is trying to frame Avril for murder and to keep her out of the clutches of her chief antagonists: Laurence's replacement, the psychotic nephew of former Commissaire Larosière, and Carmouille, although she eventually saves the day.