Faced with a series of grisly unsolved murders, a police commissioner turns to imprisoned serial killer Jeanne Deber and her estranged son for help.
As a furious Damien tries to figure out what his mother is up to, a clue found on Séverin's computer leads the team to the next potential victim.
Damien uncovers a secret that sends him racing back to his childhood home. Unable to shake her suspicions, Lucie digs into her husband's past.
The Mantis makes her next move, Achille finds a crucial clue linking the victims, and Damien pays a visit to his mother's psychiatrist.
When Jeanne receives a live video stream of the next victim, the team scrambles to stop a murder. New clues to the killer's identity emerge.
With the clock ticking and his family in danger, Damien weighs an offer from the killer. A rescue mission takes an unexpected turn.