A triple murder was committed within minutes. Vincent Revel and Mélanie Rousseau are responsible for this delicate investigation. Soon, they trace a BAC policeman, a man with personality disorders, who could be the perpetrator of the massacre. This discovery deeply disturbs Revel, and for good reason: he knows the suspect well since it is his half-brother, with whom he has not had any contact for quite a few years. He is shocked to find that this one has the same pathology as their mother ...