The underpass in Belfast's city centre may not be the most salubrious of locations, but you know when Steve Arnott and Kate Fleming - with a bonus appearance from Ted Hastings - pop up, you're in for a Line of Duty revelation. Even though we believe the show's events are taking place in a Midlands town, spotting the locations close to where we grew up and live makes watching the show even better.
Line of Duty has been clocking up applause from the moment it started. Its opening episode of series six was, in March, the most watched episode of drama since 2018, with consolidated figures showing a total 13.1 million viewers tuning in. An impressive figure, and one further enhanced when you consider 12.1 million tuned into the finale of series five. Last Sunday, the programme recorded its most watched episode - 11 million viewers and 51.7% of the audience share. More people watched the AC-12 investigations in the UK than watched The Oscars in the United States (9.85 million).
But what has brought Line of Duty into our homes and our hearts?
"It's debatable TV," says Head of Production for Northern Ireland Screen Andrew Reid. "My wife and I sit and watch. I have to say, in Northern Ireland Screen, the staff are all fans as well. We have access to quite a lot of things… but nobody does. We want to watch it when it goes out and enjoy it with everybody. Obviously we do our due diligence, we do our job as required, but we also want to sit and enjoy it.
"We sit and say, 'Ah, but what about X?' 'But the evidence came from Y.' That's the brilliant thing. [Showrunner] Jed Mercurio's mind is just incredible. Every time I think I've got it nailed, I know what's going on, I'm completely wrong, I cannot be further from the truth."
The show also challenges viewers - a millisecond glance at a post-it note in one episode will be the very thing to blow open an interrogation in the next.
"We like being challenged," says Andrew. "There's an awful lot of drama out there that is not challenging, that doesn't give you the chance to use critical thinking processes, doesn't make you think, 'But hold on, X or Y'. There's a lot of very safe, easy going TV whereas with Line of Duty, you switch off afterwards and have a discussion - and then find out that you're completely wrong."
"My husband and me watch it religiously," says Grainne McGarvey, owner of Pulse PR. "It builds every week and you're getting to the point where even though you don't really understand some of the acronyms, and everything is going on, my heart is beating on my chest on a Sunday night! You're sort of trying be calm to go to bed and you get very excited to see what's going to happen.
"Some shows let you stream the next episode but it's quite crafty the way they don't, and so there's the build-up and anticipation for the following week."
From a PR perspective, Line of Duty has made Belfast an attractive proposition for local viewers and those around the world.
"People in Northern Ireland love it so much because I suppose everybody spends time trying to identify some of the locations," says Grainne. "The city itself has been showcased: the Invest NI building, Central Library, Tates Avenue, all kinds of places. From a tourism point of view, fans want to come to see the locations."
There's no question how much Game of Thrones has impacted positively for Northern Ireland - in 2016 alone, 120,000 visitors to the country were influenced by the show. Is there a similar, if smaller, Line of Duty effect?
"There is, it's slightly smaller," says Andrew. "Whenever you have a successful show that captures people's imagination, of course it does have an effect. Line of Duty is one of those shows that just builds and builds. It's an amazing piece of writing from Jed Mercurio, wonderfully brought to life by the fantastic talented crew."
Andrew goes on to explain the positive economic impact of filming AC-12's goings on in Northern Ireland.
"For every pound that NI Screen puts into bringing shows to Northern Ireland, we have an expected return - that's direct spend measured from the budget.
"There's not just screen personnel, it's not just screen workers who benefit from it, it's the hotels, the taxis, the restaurants.
"Line of Duty has 1: 11 ratio, so for every pound that Northern Ireland Screen puts in, Northern Ireland PLC benefits from £11 coming back into the economy, and that's direct measured spend."
Grainne agrees to the show's popularity. "Even though it's not on that scale [of Game of Thrones], it still shows that people want to see where things are filmed."
While a boost to the economy is to be celebrated, so too is the reputational impact of the police procedural drama.
"Reputationally, it's good for Northern Ireland to be associated with something so positive, to show that it has so much going for it aside from all that sort of stuff," says Grainne, speaking of recent events.
"In Belfast, there's one section [that] people see it from a violence point of view, and another side, people see it as having such positive opportunities here from a filming point of view.
"Jed Mercurio said it was a fantastic opportunity to film here, everybody was so lovely, so accommodating and the local communities were completely into it. You can't buy that PR."
While locals have bragging rights about certain locations - who hasn't said they did their GSCE coursework research at one time in Central Library - that very sense of being close to home is vital to its success in Norther Ireland.
"It becomes our show, doesn't it?" says Grainne. "It's almost making us in the know - you always know somebody who knows somebody who saw it being filmed. It's like two degrees of separation, which makes it more real for people here." She describes the long-term PR opportunity, even after the show concludes, as important.
"It's getting people here and maybe they'll tell their friends and come back.
"Plus, the stars of the show have really gotten on board with Belfast, even supporting the Belfast Celtic Young Men and Ladies Club football kits [with AC-12 printed on the shirts].
"You see them on their social media, taking pictures of murals, really getting into the swing of Belfast life. It does all add to the fact that Belfast is a good place to live and people are friendly and, setting aside everything bad, there is positivity."
We can hope that, when things return to a semblance of normality, Line of Duty superfans will flock to Belfast to walk in their favourite characters' footsteps.
"There has been great excitement around the new series of Line of Duty, with thousands of viewers tuning in to hear Superintendent Ted Hastings' infamous one liners and also spotting the various locations and landmarks across Belfast as AC-12 hits the streets," says Nicole Stevenson, Screen Tourism Officer for Tourism Northern Ireland.
"Visitors seeking out landscapes and locations they see on screen has been a huge growing trend, and for Line of Duty fans this is no different. When it is safe to travel again, visitors can book a staycation in Belfast to follow the tracks of the cast, from Cathedral Quarter to Titanic Quarter, the graffiti underpass, and much more."
The size and filming opportunities now make Belfast an attractive sell for other productions, says Andrew.
"This is one of our major pitches when we're selling Northern Ireland to people, that it is a small, compact region with a very diverse set of locations.
"Belfast is a small city; in global terms it's a small northern mill town but because of the way it's grown over the years and changed importance and become the principal city, it's had possibly a lot more diversity and it's changed purpose.
"It was a very industrial city and it's become a much more administrative city. Those changes have shaped the way that the way the city looks.
"Also in the last 25 years just the city has changed so much, and there are incredibly impressive buildings and there are of course more modest domestic settings. It is usually quite easy to get around - but let's not talk about rush hour!"
If the Line of Duty effect is a love and appreciation for Belfast, then its legacy is the development and promotion of home-grown, indigenous talent.
"Has life got easier? Of course, success breeds success, there's absolutely no doubt about it," says Andrew about pitching Northern Ireland as a viable filming location to outside production companies.
"The next iteration of success as we're thinking is, of course, the development of local stories by local writers.
"One of the big things that we're looking forward to is Blue Lights, another police procedural but this time set in Northern Ireland, written by the team who wrote The Salisbury Poisonings who are from Northern Ireland. That's the next iteration, that's what Line of Duty and other successful shows give us.
"It's not the first drama to ever be commissioned out of Northern Ireland but it is it is a step up. This is primetime, BBC drama that has been written and produced out of Northern Ireland.
"We've also got Hope Street which is shooting at the minute, again a police procedure but a daytime drama. It's what we hope will be our returnable, sort of high volume returning series for Northern Ireland. We're talking 10 episodes a year - so it's not quite soap level, where you're getting two half-hours per week."
Hope Street will be seen as the 'training ground' for local talent.
"The series has been written by new and emerging writers from Northern Ireland, the production team being made up with people who are stepping up into those positions, the craft technical team, again, entirely [from] Northern Ireland."
And while we will celebrate the two new shows, the hope is that it becomes the norm, with excellent locally created content being produced year after year.
"We're trying to bring an industry in a sector for everyone in Northern Ireland to be part of and identify with," says Andrew. "It's not a niche little thing that only a few very lucky people get to be part of, it is a growing industry, it's a growing sector and the opportunities are there for all.
"That's something we're very, very keen to push out and if Line of Duty opens people's eyes to give them the interest that, 'I want to be a part of this' or, 'That looks like something I'd like to do,' other benefits come from that."
It's been decades of hard graft from organisations like Northern Ireland Screen to promote the viability of Northern Ireland as a filming destination. While there's now momentum, no one can be complacent.
"We've got an amazing crew, amazing cast, world class facilities. Belfast Harbour Studios are world class," says Andrew. "And Northern Ireland is just beautiful."
Finally, thanks to Line of Duty, the world has gotten a full appreciation of the wonder of Ted Hastings' phrases coined by the brilliant Adrian Dunbar.
"I was giving her lessons in Tedisms and Ulsterisms, that's the level of which Tedisms are seeping into everyday life," says Andrew, referring to a conversation with a TV executive. "You know that you've made a cultural hit whenever the 'isms' come into your everyday life."