Series three welcomes back Daniel Mays and Stephen Graham as the AI-enhanced “supercop” DI John Major and his long-suffering partner DI Roy Carver, along with Anna Maxwell Martin, Rosie Cavaliero, Michelle Greenidge, Richard Gadd, Amanda Payton, Tracy-Ann Oberman and Michael Armstrong. This series also introduces to the cast Vinette Robinson as Professor McAllister and Daniel Lawrence Taylor as journalist Searle.

When one of SIU’s own is murdered, Major and Carver become hellbent on solving the case and proving their worth. But it’s bigger than they thought. Forensic psychologist Professor McAllister is brought in to work the case; but still the killer manages to evade capture and wreak havoc. Can they hunt the killer down before it’s too late?