Commander Raphaëlle Coste visits the police records bureau and meets the brilliant but unsettling young Astrid, who gives her a helping hand.

Raphaëlle and Astrid take an interest in a former resident of the mysterious house, a woman who murdered her entire family there 24 years ago.

When a man collapses on a bus, possibly killed by an extremely contagious disease, the duo ends up confronting the leader of an eco-terrorist group.