The lifeless body of Antoine Garrel is found on display in a shop window in the neighborhood, hands and feet bound, with a gagged mouth. A psychologist specialized in couple therapy, he had no lack of enemies among his clientele of cheating husbands and crabby wives. Among his patients, one couple had just suddenly stopped therapy - and with good reason. Showing up a bit early for their session, they found Garrel in his office, in an compromising situation with his mistress. An affair the dead therapist's wife knew nothing about. While her team works to identify this woman, Chloe asks Hyppolite to look into the crime methods of the murder and discovers two other men had been assassinated under similar circumstances in Belgium. To the amazement of all, the investigators find evidence that the serial killer is none other than a woman suffering from postpartum depression; but Chloe has a hard time subscribing to that theory.