Major and Carver reunite, but tensions remain high. When a police officer is murdered, Carver becomes hell-bent on solving the case, Major has an epiphany and resolves to become a better man, and both detective inspectors are out to prove themselves.

With a serial killer at large, Major and Carver call on the help of forensic psychologist Professor McAllister. Parfit worries about Major's AI updates.

Major faces an outside threat to his AI, and Carver contends with a serial killer's twisted games.

Major and Carver begin to close the net on the killer when a witness provides a shocking revelation.

Chalmers, the former police commissioner who has plagued Major since the day he was reanimated, faces trial. With Major busy testifying, Carver is running out of time to decipher the latest clue and save the killer's next target.

With time running out and suspicions running wild within SIU, Carver must clear Major's name and thwart the killer's final revenge.