In the small town of Fermont, Celine and Alexandre must solve the murder of a woman who was found inside the city's "wall," wearing a Chinese mask.

Celine and Alexandre make progress with the investigation; they learn that on the night she disappeared, Justine left the bar with a mysterious man.

Celine is now interested in looking into the murder of young Gregoire three years prior, as the two deaths are linked by method, among other things.

Celine believes that multiple murders are connected, while Jacques refuses to admit there's a serial killer and doesn't send reinforcements.

Celine begins to understand the killer: he murders people who are already victims in some way; in the meantime, Anthony and Raphaelle are on the run.

A new disappearance worries the police and Dave doesn't show up for work; meanwhile, the fleeing duo is caught, and Anthony makes troubling confessions.