In an old industrial unit on Belfast's Edgewater Road, filming of BBC2 crime drama Line of Duty is nearing completion. For several summer months, the warehouse in the docks area has been home to the series' production office. Today, it doubles up as an interrogation room, used by an unspecified police force based somewhere in England's Midlands.
Several miscellaneous scenes are being played out, featuring actors Martin Compston (DS Steve Arnott) and Vicky McClure (DC Kate Fleming). The pair were first seen teaming up in series one to weed out corruption within the police.
Under the leadership of Superintendent Ted Hastings, portrayed by Fermanagh actor Adrian Dunbar, the baby-faced DS Arnott and DC Fleming joined forces to investigate 'model cop' Detective Chief Inspector Tony Gates, of the serious crime unit, TO-20.
Although series one centred on Gates, the grisly finale meant a new target for anti-corruption (AC-12) had to be introduced next time round. Step up Detective Inspector Lindsay Denton, played by new addition to the cast, Keeley Hawes.
Series two of Line of Duty has opened in explosive style, when the ambush of a police convoy leads to the deaths of three police officers and serious injuries to a protected witness. As the sole surviving police officer, DI Denton is initially the anti-corruption unit's most valuable witness. But as the investigation goes on, suspicions begin to arise that all is not what it seems.
The show's creator Jed Mercurio, who was on set throughout the entire shoot, concedes that many fans were disappointed that Lennie James, who played Gates, would not be back for series two.
Explaining his reasons for bringing in a new character for investigation, he says: "The original pitch I made to World Productions and the BBC was that Line of Duty would have a unique format for a returning drama.
"The investigators would return from series to series, but each time they'd investigate a different police officer accused of some form of corruption. The case would play out as a serial over the run of the episodes and reach a final irrevocable climax for the guest star."
Mercurio said he wanted Keeley Hawes' character to be as far removed from Tony Gates as possible. On the surface she appears to be mild mannered, socially and professionally isolated.
He says: "Because she is the sole survivor of this violent ambush she starts out being the most important witness but as things proceed, the team starts to suspect that she might be hiding something. This is what drives the whole series. Is she an innocent victim of the ambush or is she part of a conspiracy?
"Her character is very complicated. At times she comes across as weak, at other times strong and dynamic.
"The big difference between this series and series one is that this one is much more of a whodunnit and there are more twists and turns."
For glamour girl Hawes, playing Denton was the most harrowing role she has ever taken on. In the upcoming series, viewers will see her character beaten and tortured while in one scene, she has her head flushed down a toilet.
It's a far cry from the Ashes to Ashes or Upstairs, Downstairs, but Hawes says she enjoyed every moment of the shoot.
"I absolutely loved it," she says. "I didn't love going into the make-up truck every day and having them look at me saying "yep, that's great!" without even brushing my hair, actually only putting a bit more dark under my eyes.
"But it's quite liberating once you get used to not even bothering to wash your hair and people just adding a bit more grease. It's really nice to have very few touch-ups between takes.
"There is one point where she has really been through the mill – by the end of that scenario, I think nobody has ever looked that bad on the television screen. It's liberating for me as I have played lots of glamorous characters and this is the absolute opposite."
When Hawes was first sent the script, Mercurio and the director Douglas MacKinnon still hadn't decided if Denton was corrupt or not.
"It was quite incredible to go in and play the scenes completely not knowing whether I was guilty or otherwise," she says. "I've never had to do anything like this before so it was really an attraction.
"Lindsay isn't the most cheerful person I have ever met. To begin with, she isn't in a relationship, she lives alone and has a very small family. Her job is her life and she is completely dedicated to it and always has been.
"She becomes horribly involved with this disaster we see in the first episode. It's tough to say anything without giving it away."
But Hawes has a lot of sympathy for her character.
"I hope the viewers like her," she adds. "She's not a bad person. We don't ever find out that much about her personally, we don't ever see her having a great time in her life or at a high point. It's difficult to know what there is to like but we are hopefully gunning for her to get out of the situation that she's in and understand the reasons why she is in it."
While the mystery surrounding her character enticed Hawes to take on the part, she says getting the chance to come to Belfast was another huge draw. The actress had never filmed in Northern Ireland before but was impressed with the place and the people.
"I loved filming in Belfast," she says. "The Northern Irish were really welcoming, and one of the nicest crews I have even worked with and I am still friends with a few of them.
"They had all just come from shooting The Fall and I believe they were also filming Dracula – it was a really exciting time to be there."
Coming to Belfast to shoot Line of Duty might have been a new experience for most of the main cast, but for Adrian Dunbar, who plays big boss and father figure, Superintendent Ted Hastings, it was an opportunity to catch up with family and friends.
The Fermanagh-born actor, who lives in London, says he was proud to be able to show off the city in such a positive light.
"There is so much happening here at the moment," he says. "You don't feel you are away from the centre of where everything is happening, because there are so many other things going on constantly and you're running into other crew and actors all the time, who are also in town.
"In terms of the film industry and what is happening here, the likes of the BBC, its head of drama, Stephen Wright and Northern Ireland Screen, all deserve a pat on the back for being able to attract a lot of work here. It's great for young people entering the industry because there are now jobs to go for. It's a good time to be here."
In series two, we are introduced to Hastings as the head of AC-12, leading the investigation into the ambush. As the series unfolds, we learn that his marriage is in trouble and that the pressures of his personal life may be affecting his work.
"It's the background noise of the characters' personal lives that feeds into their public work that makes this series different to the last," explains Dunbar.
"This time round, Ted is compromised by who he is going after and by what is happening at home. It's not quite a black and white story line for him.
"But he is still very much the moral compass of the show. He is very old school and holds old school values. Well, that's the way he came across to me and that is the direction I pushed him in."
He adds: "It might help that he's from Northern Ireland. His accent certainly gives him an air of authority."
Dunbar says the script second time round is "even better, very dramatic, with lots of twists an turns". But it says what makes Line of Duty such a stand-out drama is the gritty reality of the writing.
"One of the great strikes of the series, I think, is that it is very real in terms of procedure. You are not watching something that is entirely made up. It's how things would actually happen in real life rather than something forced along for dramatic effect.
"Even though it is hugely dramatic in terms of its story lines, it follows a very factual, procedural route."
Dunbar says he was thrilled to work again with both Arnott and McClure, whom he describes as young actors "at the top of their game". Series two also reunites him with Hawes, whom he worked with previously in his role as Martin Summers in Ashes to Ashes.
"Keeley is a fabulous actress," he says. "I was looking forward to seeing her play this role and I think she brings a huge amount to it.
"We've got a fantastic script written by one of the best writers out there at the moment in Jed Mercurio. I'm working with some fabulous actors all the time, and I think the series has a lot of merit because of its authenticity. You put all that together, and I just feel very lucky that I'm involved with it."
A significant difference in this series is the choice of location. While series one was shot in Birmingham, the cast relocated to Belfast to film series two. As well as the warehouse at Edgewater Road, filming also took place over a number of weekends at an office block occupied by Invest NI (AC12 HQ), while the exterior of Central Library doubled up as the facade of police headquarters. The setting for the story, however, remains undisclosed.
"For legal reasons the BBC did not want us to set the drama in a specific city because it deals with the sensitive issue of police corruption," says Mercurio.
"In terms of locations, local cast and crew, we had a great experience shooting in Belfast. It doubled seamlessly for our anony- mous English city."
Scottish actor Martin Compston, who plays DS Steve Arnott, admits moving to a new city to shoot was not without its problems.
As we sit in his trailer between takes, he explains: "It was quite a tough shoot. Moving to Belfast felt like we were starting all over again, when we'd been in a rhythm. But it was a great set in Belfast and if we do come back, I will look forward to it.
"I really think series two promises to be bigger, better and bolder than series one. We've taken it to the next level."
In series one Arnott initially dislikes the idea of investigating other police officers. But his eyes are opened to corruption and he returns with more confidence in the new series.
"Steve is pretty arrogant at times because he thinks he's so good at his job," he says. "He's the rising star of anti-corruption and plays up to this. He gets away with a lot of things because the people around him, especially his boss, think he's so good.
"I like him, though he's not completely likeable. But I enjoy playing him, for those reasons.
"Steve is also very dogged and can be a bit fearless, which can lead him into trouble. If he thinks someone is in his way, he'll go after him. In series two, he comes back as a bit of a bloodhound."
Arnott enjoys a close relationship with DC Kate Fleming, played by This Is England star Vicky McClure. Compston says one of the reasons he agreed to sign up for Line of Duty was the chance to work alongside McClure, whom he describes as the UK's best young actress.
"I love working with Vicky, she's brilliant. We bounce off each other on screen," he says.
This time, however, Arnott is teamed up with a new partner, DC Georgia Trotman (Jessica Raine) as Fleming has personal reasons for feeling uncomfortable about working on the new case. And this series delves deeper into the characters' own lives, revealing that Arnott is a bit of a ladies' man.
"Steve thinks with his trousers and gets carried away quite a lot," laughs Compston. "It's something that Keeley's character exploits very well."
While Lindsay Denton takes advantage of Arnott's weaknesses, DC Fleming's relationship with him goes from strength to strength. They are dedicated to each other and work well as a team, though Arnott's eye for the ladies is a slight annoyance to her.
"She doesn't want to see him get distracted," explains Vicky McClure. "She wants to see him stay focused on the job.
"There are definitely some really nice scenes between Steve and Kate. He helps her out quite a lot with the troubles she has with her family and ends up giving her a place to stay
"The great thing is that it's not a sexual relationship at all. Steve has his own thing going on with many ladies in the show! It's nice to see they have a genuine friendship and outside of work – I think they are really good mates.
"With Steve, Kate and Hastings (Dunbar), there is definitely an element where their personal lives are affecting their work. The majority of the drama is based on the case but it does show what goes on behind the scenes as well."
McClure said she was drawn to the drama because of the quality of the script. "In Line of Duty, the script is the star," she says.
"It's so well written, though quite wordy and contains a lot of police jargon. The challenge is to make it sound powerful and convincing, so we all have to be well prepared and know our dialogue by heart. If we're going to convince, we can't be stuttering over words because that would just slow the pace down."
To ensure the script was true to life, Mercurio drafted in a police advisor to help out with the language. One of the most daunting experiences for McClure and several other cast members was an 18-page scene, which required intense study and concentration. The actors were all nervous in the run-up to 'D Day', anxious that they may forget their lines and mess up such an important scene. But after several takes, they managed to shoot it.
McClure says: "The following day, we had to do it all over again, to get different angles, and because it was so engrained in our brains by that stage, we did it perfectly. We all thought 'why didn't we shoot that one instead?'"
While Fleming gets on well with her male colleagues, her relationships with the female characters are trickier. New cop Georgia Trotman is bright and ambitious and takes over the case when Fleming backs off. Lindsay Denton is a more complex character and difficult to break down, though McClure says she had great fun playing scenes with Keeley Hawes.