'Line of Duty' Season 4 refresher — everything you need to know

Line of Duty season 4
Line of Duty stars Thandiwe Newton, Martin Compston, Adrian Dunbar and Vicky McClure. (Image credit: World Productions/ BBC / Aidan Monaghan/ Des Willie)

Line of Duty Season 4 hit our screens in 2017, and saw Thandiwe Newton joining the cast as DCI Roseanne "Roz" Huntley. This character became the main subject of investigation during this season, following the big revelation in Line of Duty Season 3 which revealed that Matthew "Dot" Cottan (Craig Parkinson) was The Caddy.

With many of us excitedly tuning into Line of Duty Season 6, currently airing on BBC One, now is the perfect time to remind ourselves of the explosive, dramatic events that happened in previous seasons. All episodes are available to watch on demand via iPlayer.

Spoilers ahead!

Line of Duty Season 4 recap — The main storyline 

In Line of Duty Season 4, DCI Roz Huntley (Thandiwe Newton) finds herself under suspicion from AC-12. Before this season begins, Huntley was appointed as Senior Investigating Officer of Operation Trapdoor by Assistant Chief Constable Derek Hilton (Paul Higgins). Operation Trapdoor saw Central Police investigating the kidnapping and murder of Baswinder Kaur, the disappearance of Leonie Collersdale and the attempted kidnapping of Hana Reznikova, so there was lots going on during this case. 

It was revealed that the Organised Crime Group (OGC) were responsible for all three incidents, specifically the "Balaclava Gang". Responsible for most deaths in Line of Duty, they work closely with the mysterious 'H', who remained a mystery until the end of season four. As well as this case, Huntley is also involved in investigating the murder of Forensic Investigator Tim Ifield (Jason Watkins).

Ifield alerted AC-12 about his suspicions when it came to Huntley, claiming she was deliberating ignoring key forensic evidence. Huntley pays him a visit after suspecting he'd accused her, and the two get into a fight before Huntley knocks her head on a kitchen counter and passes out. Ifield panics and, believing she's dead, tries to cover up what he's done. But Huntley regains consciousness and inadvertently kills Ifield with the power saw he intended to dismember her with! Gruesome!! Following this, she does everything in her power to try and cover up his murder.

Meanwhile, Derek Hilton was revealed to be a bent copper who was secretly working with the OGC. He had been blackmailing PC Maneet Bindra (Maya Sondhi) , who reluctantly provided him with classified AC-12 documents in an attempt to make them look corrupt. She was doing this in an attempt to protect her cousin Vihaan Malhotra (Maanuv Thiara), a problematic member of Central Police.

What happened to Roz Huntley?

It all goes wrong for Roz Huntley by the end of Line of Duty Season 4. Despite her best efforts to conceal the truth about Tim Ifield's death, including pinning the blame on her own husband Nick. As well as this, her hand had been amputated after suffering a serious injury during the fight with Ifield. She discharged herself from hospital, and was arrested by AC-12 soon after for Ifield's murder.

As of episode 6, she has been serving a 10 year prison sentence for the manslaughter of Ifield and perverting the course of justice.

Line of Duty Season 4 recap — What happened to Derek Hilton?

Derek Hilton clashes with Ted Hastings (Adrian Dunbar) in Line of Duty Season 4, even going as far as to accuse him of being 'H' after discovering DI Matthew Cottan's (Craig Parkinson) dying declaration in the files obtained by Maneet. The declaration revealed that Cottan had been working for a corrupt officer within the force, known simply as ‘H’, and that he had been the caddy.

However, Hilton is later found dead and the cause is ruled as suicide, but it appears it was actually staged by the OCG which indicated they were trying to keep him silent.

Is there a trailer for Line of Duty Season 4?

There's no trailer online, but you can watch an official teaser for the first episode of season 4 below.