Line of Duty recap: What happened in series one to five?

Line of Duty is set to return to BBC One for its highly anticipated sixth series.

The crime drama, created by Jed Mercurio, has been one of the most watched British series of the past decade, with viewers across the nation hooked by its twists and mysteries.

The first five outings have seen some impressive actors join the show, but in Line of Duty, you can never be sure anyone is safe from meeting an untimely end.

With series six expected to debut on BBC One on 21 March 2021, here’s a recap of everything that’s happened in the first five runs of the show…

This may be stating the obvious, but *spoiler warning* for those who don’t wish to find out what happens in Line of Duty series one to five.

Series One

In the first season of the show, we are introduced to DS Steve Arnott (Martin Compston), as he refuses to help cover up a botched police raid that resulted in the shooting of an innocent man. His integrity is noticed by Superintendent Ted Hastings (Adrian Dunbar), who enlists him into a radical anti-corruption police unit known as AC-12.

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His first case is that of DCI Tony Gates (Lennie James), a hotshot officer whose shining arrest record seems to be hiding something suspicious.

Working with Arnott is Kate Fleming (Vicky McClure), whose undercover operation helps unearth a deadly hit-and-run which involved Gates.

After the investigation comes to a violent end - with Gates taking his own life - we learn that another officer in the team, DS Matthew “Dot” Cotton (Craig Parkinson), is hiding connections to shady underworld figure “Tommy” Hunter (Brian McCardle).

Series Two

Season two opens dramatically as a police vehicle is ambushed while transporting a prisoner under witness protection, whom we later learn is Hunter. Several police officers are killed, along with Hunter himself.

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DI Lindsay Denton (Keeley Hawes) manages to survive the attack, but becomes a suspect in the ensuing investigation.

The attack was in fact organised by Cottan, to conceal his secret identity as the corrupt police mole known as “The Caddy”.

Denton is sent to prison for her minor role in the attack, while Cottan is brought onboard the AC-12 team.

Series Three

The third series begins with another raid gone wrong, this time involving Sergeant Danny Waldron (Daniel Mays), who kills an unarmed suspect. After manipulating the evidence to make it look like he was fired at first, Waldron becomes the subject of an AC-12 investigation.

Waldron is killed soon after in suspicious circumstances, but only after disclosing to Fleming that he had a list of perpetrators of a child abuse ring.

Cottan manages the list with Hunter’s name on it, and destroys it, all while framing Steve Arnott as the police mole behind the “Caddy” alter-ego.

The renegade rozzer fails to get away with his crime, however, thanks to DI Denton, who has been acquitted of her conspiracy charges.

Denton emails the list to AC-12, but is killed by Cottan while doing so.

After being interrogated by AC-12, Cotton eventually escapes, only to meet his death at the hands of a criminal associate, as he intervenes to stop Fleming being shot.

In his dying breaths, Cottan reveals something important to Fleming, which she records on her phone.

Cleared of all suspicion, Arnott is sent back on duty, and the child sex ring perpetrator is convicted.

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Series Four

Line of Duty’s fourth series turned the spotlight to DCI Roz Huntley (Thandie Newton), as she hunts down a serial killer.

Forensic specialist Tim Ifield (Jason Watkins) first brings Huntley to the attention of AC-12, calling her capture of the killer into question.

When she (rightly) suspects that it was Ifield who dibbed her in, Huntley confronts her co-worker. Ifield soon shows up dead (and missing three fingers), and Huntley returns to work with a suspicious hand injury.

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Arnott, meanwhile, is attacked by a mysterious masked assailant, who pushes him down a flight of stairs, badly injuring him.

Huntley eventually cops to killing Ifield during a fight, and is sent to jail for his accidental manslaughter.

We also finally discover what Cottan said to Fleming before he died: he alerted her to the existence of a corrupt officer inside the police department who is ring-leading the conspiracy, whom he is able to name only as “H”.

Read more: Line of Duty series six trailer released ahead of show’s return this month

The identity of “H” is a tough riddle to crack, however, with Ted Hastings and ACC Derek Hilton (Paul Higgins) floated as possible suspects, among several others.

There’s no real evidence on anyone, however, and Hilton falls out of the picture when he is killed at the end of the series.

Series Five

The mystery of “H” remains at the core of the show throughout its fifth series, which adds DS John Corbett (Stephen Graham) to the mix.

Series five begins as AC-12 are tasked with bringing down the OCG (organised crime group) who attack a police convoy.

It emerges that Corbett was behind the raid, because he had been going undercover as a criminal to learn the identity of “H”.

He is, however, double-crossed by another OCG figure, Lisa McQueen (Rochenda Sandall), and meets a grisly end.

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Following Corbett’s death, Hastings is investigated, leading to his suspension and a conspiracy charge brought on by DCS Patricia Carmichael (Anna Maxwell Martin).

After exposing lawyer Gill Biggeloe (Polly Walker) as a member of the OCG, however, Hastings is reinstated as the figurehead of AC-12.

The series ends with Corbett’s killer Ryan Pilkington (Gregory Piper) enrolling as a student police officer, McQueen being let off the hook with an immunity deal, and the mystery of “H”, now thought to be a group of people rather than a single individual, still very much up in the air.