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.