Tragedy strikes at Beaufort College when a gunman opens fire, killing several students before taking his own life; the lives of the killer's family fall apart as they try to understand what could have led their son to commit such a brutal attack.

Tensions continue to rise at the Tremblays, as Lea, Jeremy's sister seems to be harbouring some secrets.

The fingerprints found on the murder weapon set the investigators on a new track; Lea finally confesses to a secret that's been eating away at her; the investigators learn more about Jeremy's personal life.

The noose tightens as investigators follow the trail of Jérémy's suspected accomplice; Sergeant Boisvert and the coroner pursue the theory of radicalisation.

The investigators get their hands on a new and disturbing piece of evidence that sends shock waves through the investigation; Jeremy's parents take steps to approach the families of the victims.