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 police make a major breakthrough and suspect Jérémy had an accomplice; as Charlie's post traumatic stress gets worse, she decides to help with the investigation and reveals some new and important details.

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.