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; Anthony and Raphaelle are on the run.

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

Celine and Alex uncover the identity of a man; a new corpse is discovered; Celine figures out who the killer is.

Celine sees the pattern behind the murders: the victim, the executioner, and the matriarch behind it all. She soon realises her daughter is in danger.

At Chateau Frontenac, a body cemented in a bath launches Céline on a new investigation.

The room in which a discovery of a person named Philippin was found was rented by a woman named Esther Smith.

Céline and Daphne discover that one of the families affected by the tragedy is staying at the hotel. The collapse claimed the life of little Felix and caused an amputation of his sister Joanie, now a young adult. The Prévost clan is reeling.

More and more suspects appear for Philippin's murder. The first suspicions fall on Prévost, who was found in a coma after attempting suicide; the attraction between Alex and Joanie is inevitable.

Nathan knows Sylvie and the Prévost family well; Daphne discovers that to avoid being removed from the case, Céline has withheld information from her linking William to Esther Smith.

The details surrounding the autopsy of Esther's body reveals that she was thrown overboard from the ferry.

Céline and Daphne discover that Esther was an engineer specialising in large structures. With a committee of experts, Esther was in charge of evaluating the options for the construction of a third link between Quebec City and its southern shore.

Céline assaults William and Jacques removes her from the investigation; Daphne continues the work; Chamfort, with financial support from QMG, was providing Philippin with the means to carry out research in the lab.

Céline, supported by Alex, discovers that Philippin was developing a high-performance concrete. Enough to crush the competition: solid, durable, and 10 times less polluting than the others on the market. A discovery that would be worth billions.