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.

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.

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.

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.

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.