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's glitchy AI seriously impacts his police work. Dr. Parfitt's solution to Major's problems lead to a troubling realisation for Dennett.

Carver and Major receive new information on the Chelsea Bridge Case – a £50 million robbery committed twenty years ago by a gang who seemed to vanish into thin air.

Carver deals with an unstable Major, and Dennett calls in a favour from Millikan Biotech. When the detective inspectors are assigned to a witness protection case with some familiar faces, Carver learns shocking truths and confronts Major.

Top cop John Major is killed after a failed operation. But then the Met brings him back - as an AI prototype.

The pressure is on in the latest assignment and failure could mean it's shutdown for Major once and for all...

To Carver's bewilderment, Major reveals that he is going to move back in with Kelly. Parfit discovers disturbing information in the AI Ethics files.

With Major's AI finally living up to the hype, Carver and Kelly come clean about their relationship. The team lies in wait to catch The Juggler.

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.

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.

Major, Carver and Kelly have gone their separate ways. Things are looking up for the AI-enhanced Major, whilst Carver is gunning for a promotion and is knee deep in a new case.

Major screws up during an investigation and Carver wonders whether to turn him in. But when he learns of the consequences, he decides to cover for him.

After he and Carver are given a new assignment by Dennett, a suspicious Major prefers to stake out Kelly's work as he has a hunch she's been seeing someone else.

When Carver and Kelly find a collapsed Major with just three hours left to live, they try to get him to accept the truth. Major is determined to solve the Chelsea Bridge case and exonerate his dad before his AI shuts down.

DCS Dennett officially reopens the Chelsea Bridge case, reuniting Major with his absent father, Clifford, who failed to solve the case 20 years earlier. As Major's AI becomes increasingly unstable, Dr. Parfit and Carver clash over the solution.

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.