A mummified body is found in a Le Havre apartment. Police Captain Ariane Sallès is put in charge of the investigation, with Gaspard Lesage and Professor Richard Valetti assisting him. Initial clues seem to link the case to another earlier one.

When the body of Dr Delubac is found in a bathing tank in the sanctuary of Lourdes, police captain Fiona Langlois teams up with investigator Maxime Gardette to get to the bottom of the shocking crime.