When DCI Roz Huntley captures a serial killer, AC-12 is alerted to a possible miscarriage of justice. Thandie Newton (Westworld, Crash) stars as DCI Roz Huntley in the fourth series of Jed Mercurio's critically-acclaimed police corruption drama. In a career-defining case, Roz is under intense pressure from her superiors to apprehend a serial murderer after months of fruitless investigation. When a young man is charged doubts around his guilt lead the chief forensic investigator (BAFTA winner Jason Watkins) to AC-12. Is Roz ignoring forensic evidence that might prove the young man's innocence? AC12's Supt Hastings (Adrian Dunbar) places DS Kate Fleming (Vicky McClure) undercover inside Roz s team and with DS Steve Arnott (Martin Compston) piling on pressure from the outside, Roz is forced to act decisively. A mother of two and wife to Nick (Lee Ingleby, The A Word), Roz will do anything to stop her life from unravelling. As suspicions mount and the case becomes ever more complex, AC12 themselves come under threat.