A dismembered body is discovered, and worries grow when DCI Roz Huntley fails to report for duty. AC-12 crank up their investigation into Operation Trapdoor, concerned that Michael Farmer will go to jail for crimes he didn't commit. With suspicions that Roz may have withheld crucial evidence, a new DCI is drafted in to run Operation Trapdoor.

Kate makes progress in her undercover role, but AC-12's investigation falters when they realise that their main informant, forensic investigator Tim Ifield, has also gone missing.

Line of Duty Season 4 Episodes...

• s04e01 - Series 4, Episode 1
• s04e02 - Series 4, Episode 2
• s04e03 - Series 4, Episode 3
• s04e04 - Series 4, Episode 4
• s04e05 - Series 4, Episode 5
• s04e06 - Series 4, Episode 6

Line of Duty Show Summary

Steve Arnott is a young officer who's fallen foul of his superiors for refusing to help in the cover-up of an operation that ended in the shooting of an innocent father. He seems ideal to join AC-12, an anti-corruption police unit, just as it starts to investigate Detective Chief Inspector Tony Gates, the regional force's Officer of the Year.