DIs Major & Carver reunite but tensions remain high. When a police officer is murdered, Carver is hellbent on solving the case.

With a serial killer at large, Major and Carver call on the help of forensic psychologist, Professor Sarah McAllister.

The body count rises and Carver and McAllister have no choice but to follow the clues and play the killer's twisted game.

Major starts to fall apart under the pressure of a compromised A.I., explosive secrets and Parfit kicking him out of the lab; a witness provides a shocking revelation, leading to a breakthrough in the serial killer case.

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

Time's running out as suspicions run wild within SIU. Now Carver must clear Major's name AND put a stop to the killer before they enact their final revenge. But who can Carver trust? And who will outwit who in the final chapter of this deadly game?