Marie discovers the severed head of a man in the coffin of a young woman. He immediately relates it to the news of a decapitated body that was found in the salt flats of Guérande.

When during a routine inquiry Marie Daguerre discovers the freshly sliced head of a man in the coffin of a young girl dead 15 years, she immediately connects it to news of a headless body found floating in the salt marshes of the Guérande in western France. Soon Marie finds herself sent to help the region's criminal investigation unit where Vincent Becker, the man with whom she shares a complicated past, is leading the investigation. Working together once again, our heroes vacillate between the pleasure of each other's company and the pain of old wounds left unhealed, as they uncover unsettling details of the case-starting with the discovery that the decapitation was carried out with a tool dating from the 15th century, and bears the mark of a wealthy, debauched aristocrat once known as "Bluebeard."—Happy_Evil_Dude