Can I Get a Witness?:Line of Duty S2.

"Maybe there are some people out there who always tell the truth and ones who always lie. The rest of us choose our moments. This is one of them" - DS Steve Arnott

On a quiet road, in the darkest depths of the night, a police convoy escorting a civilian under the witness protection programme is attacked and everyone in that convoy, except DI Lindsay Denton (Keeley Hawes), is attacked and killed. As the organiser of the convoy, Denton immediately becomes under suspicion and AC-12 are assigned to investigate if she, or any other police officers, had been involved in tipping off the perpetrators of this crime, of these murders.

Line of Duty series two (BBC/iPlayer, creator and writter:Jed Mercurio, episodes directed by Douglas MacKinnon and David Nettheim) originally aired in 2014 and, over the past seven years, it's lost none of its bite and the arc of character development is even more intricate and finely drawn than in the first series. 

We get a closer look at the personal lives of the key players. DC Kate Fleming (Vicky McClure) is having a very risky affair, the love life of DS Arnott (Martin Compston) is even busier, if less damaging, and Superintendent Ted Hastings (Adrian Dunbar) is shown to have an uneasy connection with his estranged wife Roisin (Andrea Irvine) who he's trying to win back with the promise of a cruise after an ill advised financial venture that has resulted in their separation.

Even new recruit DC Georgia Trotman (Jessica Raine), it is hinted, has quite a 'thirst'. Trotman's joined the team because when Hastings read, to them, the names of those that died in the ambush, Fleming's eyes lit up at the mention of the name DS Jayne Akers (Allison McKenzie). Fleming asks to be taken off the case because she went through police training with Akers (which she tells Hastings) and because the person she's been having an affair with is Akers' husband Richard (Niall Macgregor).

Something she chooses not to tell Hastings. Arnott and Trotman warm to each other after initial disagreements about how AC-12 are approaching the case against Denton. It is revealed that Denton is in huge and, vitally, undeclared debt which in the eyes of Hastings and Arnott (if not, initially, Trotman), make her susceptible to bribery.

Did DI Lindsay Denton receive money from people with a vested interest in killing a potential witness and which resulted in the death of three police officers? This is the crux of a complex, and compelling, story that unravels to reveal a world of bullying, revenge, senior police leaking to journalists, prison guards so sadistic they'd scare Vinegar Tits from Prisoner:Cell Block H, waterboarding, "vice", gym equipment being used as improvised torture devices, faces shoved into toilets, and lonely crisp sandwiches at quiet work stations.

When Denton is transferred, by Chief Superintendent Mallick (Steve Toussaint), to a missing persons unit, Fleming, now back on the case and working undercover, is assigned as her assistant as they get to work searching for missing teenager Carly Kirk (Charlotte Spencer) who, it is feared, may have been murdered.

Against the usual Line of Duty scenes of taped office interviews, pub chats, whispers, text messages, lanyards, people scrolling through databases full of mugshots, and of cars moodily driving through underpasses to Carly Paradis' ominous piano score and the squawk of police radios, a mercurial story is constructed that can, at times, be genuinely chilling (I felt chills go up my back more than once and not least during a gripping scene in an intensive care unit) and, on other occasions, highly moving.

Which is right and proper. Because even though murder and other violent crimes are play out as gripping drama, the makers of Line of Duty never let you forget there are victims of these crimes. Something that gives Hastings plenty of opportunities to say "mother of God" in disbelief but, also, something that allows a meditation on just who the victims are.

While, in Line of Duty, there are some out and out bad guys, there are many others who are merely compromised by their own history, their own foibles, or their own circumstances. Be they financial, romantic, or merely as result of their misguided lust and greed. Even the most well meaning players, those of AC-20 for example, are walking a precarious tightrope between doing what they know is the right thing and what they believe is the right thing for themselves.

Some suffer for the decisions they make, others are yet to do so but seem likely to in future series, but very few suffer quite as much as Denton here. As her world starts to implode, rightly or wrongly, she faces the wrath of her superiors and the anger of her peers, she finds herself wearing a neck brace after a car accident, and is fed actual shit in prison.

Which makes her vomit. Keeley Hawes is superb as Denton. Eating sad lonely meals of pasta (or, indeed, shit) and playing the piano in her modest flat, having violent confrontations with her noisy neighbour, and leaving us, the audience, constantly second guessing both her motivations and whether or not she is guilty of the crimes she's being accused of, innocent of them, or stuck in some hellish limbo between the two.

At times she appears vulnerable, troubled even. But it's not usually long before she switches to a more calculating, menacing, even dangerous, mode of behaviour. Is she simply trying everything to protect herself and/or prove her innocence or is she, quite simply, conniving, dishonest, and an accessory to murder?

DCC Mike Dryden (Mark Bonnar), DCS Lester Hargreaves (Tony Pitts), DS Nicola 'Jolly' Rogerson (Christina Chong), DS Manish Prasad (Sacha Dhawan), DC Jeremy Cole (Henry Pettigrew), and Tommy Hunter (Brian McCardie), as well as the returning DI Matthew "Dot" Cottan (Craig Parkinson) all prove crucial, or at least relevant, to the story's unravelling but it is Dunbar, Compston, and McClure again who do the bulk of the heavy lifting.

As in series one, they are outperformed by only one player. Hawes, as Denton, takes over from Lennie James (DCI Tony Gates) in series two, both as the prime focus of AC-20's investigations (though far from the only suspect, this apple is already starting to look rotten to the core) and as the most powerful performer on the screen. Quite often, in Line of Duty, you will see a man or woman descend in a lift and that physical journey will, somehow, represent an analogue for the downward journey their life, and/or mental state, is taking. It is to Keeley Hawes and everyone else involved in Line of Duty S2's great credit that we're never sure if that spiral can be arrested. Or, in fact, who else might get arrested at any given moment.