When DCI Roz Huntley captures a serial killer, AC-12 is alerted to a possible miscarriage of justice. Thandie Newton 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? AC-12'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), Roz will do anything to stop her life from unravelling. As suspicions mount and the case becomes ever more complex, AC-12 themselves come under threat.