AC-12 turn their attention to DCI Roz Huntley (Thandie Newton) after a forensic officer alerts Steve Arnott of potential holes in a murder investigation. Gripping fourth series of the acclaimed drama.
Thandie Newton stars in the fourth instalment of the crime drama as a detective on the trail of a serial killer. She is determined to catch the culprit as soon as possible and prove her worth to her superiors - but a colleague fears her efforts may have led to a miscarriage of justice, and alerts the AC-12 team to the situation.
A new DCI is placed in charge of Operation Trapdoor as Roz fails to report for duty. A dismembered body is discovered, and the AC-12 team delves deeper into the case as evidence mounts up that an innocent man has been convicted of crimes he did not commit. Kate makes progress in her undercover role as all the signs point to crucial evidence being covered up by Roz, but the investigation suffers a setback when the team discovers that the main informant, forensics investigator Tim Ifield, has gone missing.
Kate is approached by another woman who claims to have been assaulted by Michael Farmer. Combined with the new forensic evidence casting doubt over Tim Ifield, the revelation threatens to undermine AC-12 team's case, to Steve's fury. However, it gives Kate the opportunity to ingratiate herself further with the officers of Operation Trapdoor. Steve challenges Roz's husband to vouch for her whereabouts on the night Tim Ifield disappeared, and sees a new direction for the investigation when he proves evasive.
Nick Huntley is brought in for questioning by AC-12, but denies any involvement in Steve's attack. However, the interrogation leads him to question how honest his wife has been with him. New anomalies emerge in the forensic evidence which cast further suspicion on Roz - who responds by dismantling the detectives' case with inside information of her own.
Nick Huntley faces lengthy questioning before being charged with Tim Ifield's murder. The AC-12 team is convinced Roz was also involved, but with Hastings coming under pressure from Hilton, the detectives are running out of time to prove their theory, and are forced to risk everything to bring the guilty parties to justice. Concluding episode of the fourth season, starring Adrian Dunbar, Vicky McClure, Martin Compston and Thandie Newton. Last in the series.