Between 1978 and 1979, the inhabitants of the Oise are in fear of a maniac who kills several hitchhikers and escape the police. He was then dubbed "the killer of the Oise" is actually a shy young policeman who will investigate his own murder, only to lose control of the situation.

Juliette is attending the baptism of Lucas, the son of her best friend Claire. But the young mother, weakened by her childbirth, shows disturbing signs of depression.