Ana is found dead, her heart torn out, just before she was to leave the psychiatric hospital where she had been sectioned. A first investigation for Angèle Maury, one she'll have to conduct alone. But how to question the mentally ill? Can they be believed? Was the murderer a patient?

Angèle discovers a worrying detail: she and Ana were both born in the same year and on same day. The autopsy reveals that Ana had had consensual sexual relations before her death. Another patient in the clinic is pregnant but has absolutely no memory of having had sex. Coincidence?

Angèle hopes to find answers in Ana's personal diary, but most of it is illegible. The patients are very disturbed and fear a new tragedy. As Ana continuously appears to her, Angèle is disconcerted by Simon, a schizophrenic patient who is also terribly seductive.

Maxime is in a coma, knocked out as he was about to reveal the murderer's name. Only Rose, the clairvoyant, can now help Angèle but she has isolated herself and refuses all contact. Obsessed by Ana, fascinated by Simon, Angèle is slipping gently "to the other side".

Maxime comes out of the coma and reveals the murderer's name to Angèle. Shocked by the revelation, she decides to say nothing, convinced that he's lying. Meanwhile, those around Angèle question her lucidity. Commissioner Favard, having discovered that she had hidden the truth from him, takes her off the case.

Angèle's mother convinces Bastien that her daughter is losing her mind and should be sectioned. But Angèle manages to escape. Certain that she knows the murderer, she persuades Favard to restart the searches. In the clinic's vegetable garden, they find what they'd been looking for from the start: Ana's heart.