Picardie, France 1964. Midnight at the exclusive and mysterious Spa St Jean des Eaux, near Poissons-les-Marais. A man is standing in the therapy pool. But he's not there for his health; someone has chained him to the bottom and let him to die very, very slowly. Along with the unusual and elaborate method of execution, the dead man has Inspector Lucas Rocco's name and number in his pocket... Patrons at the Clos du Lac refuse to speak and the ministry...