Police detective Franck Mercoeur arrives from St.Nazaire with his deputy Olivier Morel to investigate when a posthumously chopped-off female hand is found in the open-air sea salt extraction of Gwenrann (Guérande) on Normandy's coast. They welcome assistance from forensic anthropologist Marion Ravel and her apprentice Maxime Nau. The scene fits the drawings of unidentified amnesiac schizophrenic 'Isabelle', a self-declared medium. The hand's (missing) wedding ring imprint and DNA confirm she must be Marie, the 90 years earlier disappeared grandmother of Isabelle's therapist Catherine Creuzot. Her husband Paul Creuzot, Franck's school friend, receives anonymously Marie's music box after Catherine disappears. Paul has an alibi. Rapist-kidnapper Grégory Bessi, the salt firm worker who reported the hand and Catherine's former patient, admits to have been paid 25,000 Euro anonymously to photograph her and dig up Marie's body.
—KGF Vissers