Line of Duty newcomer Kelly Macdonald says she struggled to understand some of the show’s complex scripts… and viewers will know exactly how she feels.
The Scots actor – who guest stars as DCI Joanne Davidson in the hotly anticipated sixth series – openly admits: “It’s the kind of detailed forensic policing that, even when I’m saying the words, I’m only half aware of what I actually mean.”
Even the read-through left her “a shell of a woman” – but that’s nothing compared to how we feel when we’re left with high blood pressure after every brilliantly intense episode.
If you’ve been equally perplexed by the first five seasons, here’s our Sunday Mirror catch-up guide to all the drama ahead of series six debuting next Sunday.
Series one
DS Steve Arnott joins specialist police anti-corruption unit AC-12 after refusing to help cover up a bungled police raid in which an innocent man is gunned down.
With the help of his boss Ted Hastings and undercover officer Kate Fleming, the unit launch an investigation into detective Tony Gates (Lennie James) who has a remarkably high arrest record.
AC-12 discover Gates helped to cover-up a hit-and-run involving his lover Jackie, who later died.
But Gates finds himself being framed by underworld gangster John “Tommy” Hunter (Brian McCardie). In the end, it turns out he wasn’t a corrupt copper after all but had made bad decisions to try to hide his affair with Jackie.
In the gripping season finale, Gates arrests Tommy but realises his career is over and walks into the path of an oncoming lorry.
We also discover that another officer in Gates’ team – DS Matthew “Dot” Cottan (Craig Parkinson) has been an inside snitch for gangster Tommy.
Series two
In dramatic opening scenes, a police vehicle – which we later discover is carrying Tommy under witness protection – is ambushed.
He is killed, along with a number of police officers, but cool-headed DI Lindsay Denton (Keeley Hawes) survives, leading AC-12 to question whether she was in some way involved.
However, it turns out that the ringleader of the ambush was none other than conniving Cottan, who was trying to protect his identity as The Caddy.
Pitiful Denton had a small part to play in the attack but, it turns out, had not realised the full extent of the plot.
Infuriatingly, she gets blamed for it all and is sent to jail so the real culprit – Cottan – gets away with it, even bagging a cushy new job in AC-12 into the bargain.
Hastings is determined to get to the bottom of it all and discover the true identity of The Caddy – unaware he’s just recruited him!
Series three
When Sgt Danny Waldron (Daniel Mays) kills an unarmed suspect during a police raid, AC-12 start investigating him.
But in a shocking end to episode one, Waldron is bumped off by one of his colleagues.
Before his death, he tells DI Fleming about a child abuse ring that operated at a home he was placed in as a kid.
He tries to pass on a list of names but it is intercepted and destroyed by Cottan.
The corrupt officer then frames Arnott as The Caddy – but a newly acquitted DI Denton saves the day. She manages to get a copy of Waldron’s list to AC-12, which reveals that Cottan is in fact The Caddy. He later tracks down Denton and kills her.
In a dramatic finale, Cottan is grilled by AC-12 but escapes and is chased by Fleming.
Just when we think she’s about to be shot by one of his criminal pals, he takes a bullet for her. In his dying moments, Cottan reveals a key piece of information, which Fleming records on her phone.
Series four
AC-12 shine their spotlight on DCI Roz Huntley (Thandie Newton] after her forensics supervisor Tim Ifield (Jason Watkins) raises concerns.
He insists there has been a possible miscarriage of justice in her team’s arrest of a suspected serial killer.
Soon after Huntley confronts Ifield at his home, he is found dead and she turns up at work with a bizarre hand injury.
Eventually, it transpires that Huntley killed Ifield during a fight at his home. She admits accidental manslaughter and is jailed – after having her gammy hand amputated.
Around the same time, a man in a balaclava pushes Arnott down a flight of stairs. He miraculously recovers but ends up in a wheelchair for some time.
We also discover that in Cottan’s final moments he told Fleming that there is a corrupt copper ringleader known only as “H”.
Hastings and another top copper called Derek Hilton – who ends up dying – are among the many possibilities.
Series five
The riddle of who could be H continues to perplex the nation– especially after AC-12 take on an organised crime group who ambush a police convoy.
They discover the man behind it is undercover police officer DS John Corbett (Stephen Graham), who claims he infiltrated the criminal gang to find out who H is.
But Corbett is double-crossed by fellow gang member Lisa McQueen (Rochenda Sandall) and has his throat cut.
After Corbett’s death, Hastings is investigated – leading to his suspension and a conspiracy charge. But after exposing lawyer Gill Biggeloe (Polly Walker) as a member of the crime gang, he is brought back in.
Corbett’s killer Ryan Pilkington (Gregory Piper) goes on to enlist as a student police officer.
But the mystery of who H is deepens as Arnott suggests the Morse code for H (four dots) is a clue H is four people, not just one.
Series six
Cast members Adrian, Vicky and Martin may have gone viral on TikTok with funny dad-dancing during filming last October, but don’t be fooled – there is very little light relief in Jed Mecurio’s script for season six.
Trainspotting actress Kelly Macdonald, 45, makes her debut as DCI Joanne Davidson, whose conduct on an unsolved murder case arouses the suspicion of AC-12. Former Our Girl actress Shalom Brune-Franklin also joins the team as DC Chloe Bishop.
Trailer footage hints that Police and Crime Commissioner Rohan Sindwhani (Ace Bhatti) could be corrupt as Hastings appears to brand him “a bare-faced liar promoted to our highest office”.
But the biggest shock of all is the idea that Fleming could actually be corrupt. Is she H?
Let’s hope that after seven stress-inducing episodes, we have more answers than questions.
