Line of Duty - Season 4

After months of hunting a serial killer, DCI Roz Huntley faces intense pressure to apprehend a suspect. Michael Farmer is caught and charged with the crimes, but doubts about the young man's guilt lead the chief forensic investigator to AC-12.

When DCI Roz Huntley captures a serial killer, Forensic Coordinator Tim Ifield alerts AC-12 to a possible miscarriage of justice.

A dismembered body is discovered, and worries grow when Roz fails to report for duty. After further questioning of Michael Farmer unearths crucial new information, AC-12 challenge the case against him. Meanwhile Arnott and Fleming continue to clash.

As shocking new evidence is unearthed, AC-12 step up their investigation in to the case against Michael Farmer. Could the real killer still be at large? Meanwhile, Detective Constable Jamie Desford joins the AC-12 team.

Roz's husband Nick is brought in for questioning by AC-12. But while Nick denies any involvement in Steve's attack, his suspicions about Roz mount. Meanwhile, AC-12 discover new anomalies in the forensic evidence and issue DCI Roz Huntley with a second Reg 15 notice. AC-12's case appears watertight until Roz starts dismantling their evidence with inside information of her own.

AC-12's future hangs in the balance, after Hilton bars them from investigating Roz Huntley. But Roz's problems are building closer to home.

The explosive series finale pits AC-12 against Roz in a climactic duel to find Tim's murderer and unmask Balaclava Man.