When the body of a young dancer is found in a small mining town, Céline Trudeau, one of the town's most experienced detectives, investigates the case.

Céline is back in Quebec City and investigates the murder of a civil engineer – found encased in concrete in a Château Frontenac bathroom. Alex, on compulsory leave for post-traumatic stress disorder, unofficially investigates the case, going undercover at the château. Sophie joins her father William to hunt industrial secrets related to the city's major engineering projects. Céline is partnered with rookie detective Daphne.

Céline traveled to her fictitious hometown of Applegrove. Alex responds to a skeleton found in her uncle's orchard, which is identified as Céline's long-missing grandmother. Céline and Alex are joined by local police officer, Johnny. The squad becomes enmeshed in feuds between local families. Complications increase when the squad finds links to the bordering abbey of Saint-Benoît-du-Lac and reinvestigate the historical murder of Céline's cousin.