JUST when you thought Line of Duty couldn't have any more twist and turns, James Nesbitt joined the series as dodgy detective Marcus Thurwell.
James plays DCI Thurwell, a senior investigating officer who was briefly mentioned in series three.
He was involved in two cases that were being probed by Gail Vella, the TV journalist whose assassination is the mystery at the heart of the current sixth series.
But, last night's episode left viewers with more burning questions.
Here, we examine the six key questions AC-12 must answer ahead of next week's penultimate episode.
Q1: Is Kate Fleming still alive?
FANS were left with the mother of all cliffhangers as hero cop DI Kate Fleming was locked in an armed stand-off with bent copper PC Ryan Pilkington.
Following a raid on a workshop used by criminals, Kate (Vicky McClure) was lured to wasteland, where she was confronted by baby-faced assassin Pilkington (Gregory Piper).
AC-12 had snapped him using a burner phone to tip off his mob pals about the raids.
Last night’s thrilling episode ended with the sound of two shots being fired, leaving viewers wondering whether it was good cop or bad cop that had taken a bullet.
Or could it be both?
Q2: Is the Lawrence Christopher case key to Gail Vella’s murder?
AC-12 initially assumed that reporter Gail Vella could have been killed because she was investigating allegations of a VIP paedophile ring.
But that wasn’t her only big story, as DI Steve Arnott learned from bent lawyer Jimmy Lakewell.
She was also probing the case of Lawrence Christopher, a young black man killed by thugs in circumstances virtually identical to those of real-life race attack victim Stephen Lawrence.
But are both cases equally important? Or does the common denominator – that the Senior Investigating Officer in both crimes was retired cop DCI Marcus Thurwell – hold even greater significance?
Q3: Is Supt Ted Hastings a bent cop after all?
WHEN DI Steve Arnott carries out forensics on £50,000 found stashed in the home of murdered cop John Corbett’s widow, he becomes suspicious about his AC-12 boss Ted, whose prints are found all over it.
And when he visits mobster Lee Banks in prison, he learns that Ted has also visited him. During that visit Lee claims Ted told him Corbett was an undercover cop placed in their mob – a fact that got him killed.
Did Ted pay the £50,000 out of guilt, or was it because Corbett is actually his son from a potential affair with Anne-Marie McGillis?
And why the lingering shot on the vintage photo of young Ted with fellow police recruits? Does he have secret associations with a dark figure as yet unknown? Could it be Thurwell?
Q4: What IS the relationship between Tommy Hunter and DCI Jo Davidson?
DNA samples belonging to this series’ main bent copper Jo, left, were last week shown to link her to a sensational figure.
This week we found out that it was mobster Tommy Hunter from series one, who was then killed in series two. But we don’t know if Tommy is Jo’s father – or another relative.
And we’re not sure why that makes her fall under the control of the current band of criminals.
Muddying the waters further is the revelation that Darren Hunter, Tommy’s son, was one of the thugs who probably attacked Lawrence Christopher.
So could he be her brother, whose existence she’s forced to cover up?
Q5: Is Chief Constable Philip Osborne ‘H’?
IT may be an obvious choice to suggest Osborne is the final villain in the network of bent coppers corrupting Central Police. But he’s looking increasingly suspect.
He’s already loathed by Arnott and Hastings, who know he’s a liar.
Now they discover he was on the Lawrence Christopher case with Thurwell.
Osborne, played by Owen Teale, below, also worked with Det Supt Ian Buckells, who we now know is in league with the criminals.
The fact he has decided to slash AC-12 by 90 per cent and merge it with two other departments suggests he wants to reduce its capability to uncover his dark past and does not want anything to threaten his future as head of the force.
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Q6: Just what is eating Det Supt Patricia Carmichael?
SHE is back with a new wardrobe, but the same old sinister smile and delivery.
After trying and failing to jail Supt Hastings last series, Carmichael, played by Anna Maxwell Martin has returned to take control of what will be left of the anti-corruption unit.
And the first thing she’s done is remove expensive surveillance on three important figures in the Gail Vella case, including PC Pilkington.
It’s a move that might just have put DI Fleming in the line of criminals’ fire.
So is she a secret baddie too? Or is she just unscrupulously out to get revenge on her old nemesis?