It's one of the most highly-anticipated television returns of the year so together with a number of other online outlets, I caught up with the stars of Line of Duty to find out more about series five.
"It's one of the most exciting series because the levels of danger are ramped right up." - Martin Compston
Since launching on BBC Two in 2012, Line of Duty has gone from strength to strength, with series four making the move from BBC Two to BBC One and averaging an incredible 9.5m viewers per episode - the highest yet!
The series for those of you who have never seen it (seriously, if you haven't, head to iPlayer now) centres around AC-12, a special unit investigating corruption within the police force.
Each series up until now has seen Detective Sergeant Steve Arnott, played by Martin Compson, Detective Sergeant Kate Fleming played by Vicky McClure and Superintendent Ted Hastings played by Adrian Dunbar, investigate a single corrupt police officer. But things are slightly different this series.
We're led to believe that the format has changed slightly this series in that you're no longer going after one corrupt cop. What can you say about that?
Martin Compston: Usually AC-12's remit is going after bent cops and that's what we've always done, but we're getting to a stage where we're chasing, what has become a mythical character, 'H' and we're not having any luck going through the cops.
So we're changing tack and going after the criminal gang who the cops have been in league with. We're going to see behind the balaclava and go after them. It's one of the most exciting series because the levels of danger are ramped right up.
Before we'd been dealing with bent coppers who have been forced into criminal acts by the situations they've found themselves in, whereas this time we're dealing with a gang of murderers. It's an exciting year I think.
Does this series reward fans more than previous series?
Vicky McClure: If you've watched from series one or if you've gone back and watched from the start - if you look hard enough, you'll find a lot more in this series in terms of returns of things and people!
This is what Jed does brilliantly. The unexpected always seems to creep up on you when you least expect it. That's definitely throughout the whole series so keep your eyes peeled.
Is Hastings still a suspect when it comes to finding out who 'H' is?
Adrian Dunbar: Well at the end of the last series there are a couple of very strange looks between myself and Vicky which would suggest that something is going on with Hastings. And that will be explored through this series - his personal life.
And he'll find himself under scrutiny. That's one strand of the storyline that's running alongside the organised crime group stuff that's happening.
Before you knew about what happens in series five, what did you think about Hastings at the end of series four?
Adrian: Those actual shots at the end of series four weren't in the script. Jed came on to direct that last bit and suddenly put those shots in and we all thought "What's this?" - "I want you to get in the van. Talk to that guy... look back to Vicky" - and I just thought "Oh my God!"
He's just given himself a little springboard and didn't tell us anything about it. That happened on the very last day of the shoot. Those reactions were practically the last thing we shot and we just thought "You git. How dare you? We've just gone through six eps and at the end of it you're making us go..."
I do think he (Jed) knows rather more than he tells us, that's for sure.
Do you ever suggest script changes to Jed?
Adrian: Bits and bobs. You come across the odd anomaly that he's missed. But they have a very good team that goes through the scripts. World have a very good team so by the time the scripts arrive to us, they're pretty watertight. But you do come across the odd anomaly where you think "No, that can't happen because this happens" or "In another series that happened..."
Martin: He's really good with us. We've played these characters for seven odd years now so we know them inside out. So if there's something where we think maybe we should go in a different direction or we should play it differently - Jed's brilliant with us. He's really really open to change it. And if he doesn't want to change it, he'll explain why.
Vicky: It's not the kind of script that you can just go off piste and go "Oh we've got this." and just improvise it because we wouldn't be able to. But in the same breath it's nice to have those moments - perhaps a more personal moment - where there isn't really any dialogue for it and we'll have a little bit of a play. Or we'll add in a "mate". "Alright mate?"
Martin & Vicky: "Alright mate?" (Both laugh)
Do you find that members of the public are constantly asking you what's going to happen?
Adrian: No. The public are very strange with us because they usually come up and say "I love the series, but don't tell me anything." I think people really like to watch it in real time and then talk about it the next day.
Then there are the whole catch-up people who are on it at the moment, but people do seem to actually like the page-turny twists and don't like to know in advance. That's one of the things that gives the show such credibility I think.
How do you keep the script under wraps on set?
Martin: The secrecy levels definitely have gone up. You used to just get sent a pack for the first series, now you have passwords and your name's watermarked so that you don't share it. But rightly so, because as well as what Adrian says, people don't want to spoil it for themselves. I've really found that the media have also been great - nobody's every gave anything away.
And people are still catching up with the series now...
Martin: Stuff like Netflix and iPlayer have gave people who have just found the show the opportunity to go back and go right through it and that's great. But at the same time, because we don't launch on them, people have to wait that week for the next episode.
They don't get to sit through five or six episodes at a time, so it's great to see people coming up with their theories during the week and the anticipation building again. We've got the bet of both worlds.
How do you feel about the catchphrases the series appears to have attracted like "fella" and "one rank superior"?
Adrian: I think it's great because that's the mark of something that's really catching the audience's imagination. I think it's good to hear regional accents. I think it's good to hear phrases and so forth. I think I've got a really good one coming up in the first up.
Vicky: You have. It's brilliant. You'll know it when you hear it.
Adrian: It's very obscure.
How do you feel about the "From the makers of Bodyguard" in the trailer? Did it irk any of you?
Adrian: Yes. Absolutely! I want to talk about this actually. I mean, how dare they?! (Laughs) They're just reminding a very huge audience that Jed Mercurio's next piece is coming up. So to that extent we think "Great! Let's get the numbers." because Bodyguard was hugely successville and did great numbers and I was in the Comic Relief bit of it.
Vicky: Even I watched that (Comic Relief) live and was like (Sighs) "Oh God, yeah..." and then he (points to Adrian) pops up and I'm like "Go on Aidy!"
Adrian: That's right. We'll get them yet!
Vicky: That's what everyone's after isn't it? They're all going "I wonder if...?"
Rochenda, what can you tell us about Lisa McQueen?
Rochenda Sandall: I can tell you that there's a big power struggle running between myself and Stephen Graham's character. We're running a big criminal gang of horrible burly men who are awful. That's about all I can tell you.
Do we found out much about what's led her to that point?
Rochenda: You don't necessarily find out her personal backstory. One of the traits of Lisa is that you never really see her true self. Apart from a few little snippets but you'll never see her backstory.
We (with Jed) decided on her backstory together which is that she probably ended up in this line of work - which is unusual for a woman - by shipping drugs across county lines as a teenager and because she's so good at it, she's raised up through the ranks.
I do wear a balaclava! I did get a special lady one to fit my barnet in. It was great fun putting it on for the first time. Epic.
How much can you say about Stephen Graham's character?
Martin: He's the most dangerous guy we've come up against by far. And Stephen's just a force of nature as an actor so it was great to be on set with him. Everyone else around sort of lifts their game when he's on. I saw the first episode and Rochenda and Stephen together are genuinely scary.
And it's weird because I know what happens... but it's good because us three go back into our AC-12 groove but we're really going to come up against it this time. I think a few bullets will fly.
The people we usually chase are cops, they're not out-and-out bad people, but he's just a criminal. He's a murderer. He's the leader of this gang, one of which threw me down a flight of stairs. They are just scary people but we're thinking this is the only way we're going to get to 'H' now. Because we're getting nowhere our usual way.
Would you say this is the darkest series yet?
Martin: Yeah. I mean, there have been some pretty dark stuff. Series three with the child abuse and because that was so prevalent in the public consciousness at the time, I think that hit a nerve with all of us, because it was something I was angry about at the time. I loved working on that series.
This one in terms of actual dangerous situations - it's definitely the scariest.
There was a lot of excitement when Jed was seen hanging out with Craig Parkinson on set. Are there any surprise comebacks?
Adrian: I think there might be a couple of surprises. But, maybe not The Caddy.
Martin: Yeah, I think the machine gun to the chest was pretty final. But with Jed's writing, nothing's ever as it seems. So there's a few surprises.
Series 6 has already been announced. Will we get resolution at the end of this series or is this part of a larger story arc?
Martin: There's a pay off for sure. The BBC have been really good to us. Ever since series two we've been recommissioned for two at a time because Jed's very adamant that he's going to be the one that finishes it. If he doesn't know whether or not we'll get seven or eight yet, he will because he needs to have that pay off for the audience who have stuck with us for all these years.
It gives him the breathing space to go "Alright, I can develop this over the next series because I know we're going to be there". That's been great.
Does he know where he's going in series six yet?
Adrian: He does. He's mapped out roughly and I think initially he'd mapped out up to series five but then because it took off in the way it did, he thought beyond that and he's still thinking beyond that. He's still managing to hold on to our initial audience and give them all these pay offs of sticking with the original arc. The original arc still keeps going.
Do you enjoy living so close to each other up in Belfast?
Vicky: I love these two guys to bits and we do look out for each other, we do cook for each other, we do help each other with lines even if we're not in that scene. We have a laugh and that to me is the most important part of any job. If you're working with people you don't necessarily get on with, it's hard work.
As much as Line of Duty is hard work, it's only because of the actual dialogue and the hours. Apart from that, it's the dream job. It is nice to get home, but I miss them. I was really bad the year before weren't I?
Adrian: Oh you were terrible, yeah.
Vicky: It was a bit dramatic, but I'm an actor. It's what I do. (Laughs)
Martin: We wake up, open our doors and their two doors are there. We've got designated rooms for each thing.
Adrian: I do the cooking, we learn the lines in Vicky's flat and then party happens in this one's (points to Martin).
There's talk about a US remake. Which American actor would you consent to losing your role too?
Adrian: I think Richard Gere would be a good fit. We're very similar in many ways. (Laughs) No, I don't know. I have no idea.
Martin: Tom Cruise, just because of my height.
Vicky: Jennifer... Oh I can't remember her name!
Vicky: JLo... of course!
Adrian: It's going to be called Line of Booty! (Laughs)
Vicky: To be fair, I do have a big ass, so... Jennifer Lawrence is who I was thinking of, but I'd rather you print JLo.
Line of Duty returns Sunday at 9pm on BBC One