It depends on the state of your romance, but Cellar Door probably isn’t your archetypal date night movie.

“If somebody swipes you on Tinder and says, ‘There’s this really sweet film I’d like to take you to’, don’t go!” laughs Karen Hassan who plays Aidie, a young girl who awakens to find herself in a Magdalene Laundry. Given that she’s not aware of having been pregnant or giving birth, it’s all a bit of a puzzle.

The film flits from one seemingly disparate nightmarish scene to another at such a furious pace that my head was spinning almost as furiously as Linda Blair’s in The Exorcist.

“It goes back and forth with the mystery revealing itself in shards,” Karen resumes. “As you get closer and closer to the heart of it, it becomes almost too scary to look at. It’s not catering to the masses. It’s one where you have to trust the audience because it’s challenging to watch. The payoff, though, is so rewarding.”

All makes (sort of) sense when it gets to the totally unexpected denouement – we’re talking The Crying Game/last episode of The Sopranos-style levels of “What in Jaysus just happened there?” – details of which I can’t reveal for fear of first time writer-director Viko Nicki taking a hit out on me.

I’d almost use the terms Lynch-ian or Cronenberg-ian to describe Cellar Door but I know you wouldn’t let me get away with that.

“It took Viko eight days to write, 28 days to film and a year to edit,” the 37-year-old Belfast actor resumes. “He was very brave and scrapped the first three days of filming after having what I call a ‘glowstick moment’ and realising how it should look. The key is how the scenes run into each other – hence all the time in the editing suite! I don’t use the word lightly but I think he’s a genius.”

Cellar Door found Karen fulfilling her ambition of appearing alongside Ian McElhinney, the veteran Belfast thesp who plays Granda Joe in Derry Girls and, more importantly for George R.R. Martin fans, Ser Barristan Selmy in 25 episodes of Game Of Thrones.

“I’ve worked with his son, Michael, in theatre and was at a party in Ian’s house, so I knew that as well as being a top, top actor he’s a lovely man,” she enthuses. “He’s definitely one of those people in the business I look up to, as are my other Cellar Door co-stars Stella McCusker, Catherine Walker and Mark O’Halloran who are all talented, much travelled character actors. Mark brought a lot of laughter to the set, which was so needed when you’re playing such heavy, traumatic scenes.”

Although set in what appears to be the ‘50s, the overriding theme of women needing to have autonomy over their own bodies couldn’t be any more contemporary.

“Yeah, I feel that myself,” she nods. “I was back and forth last year, but was here enough to follow Repeal first-hand, and was thrilled with the outcome. I just wish Northern Ireland were part of it. The voting system is antiquated and tribal, and masks the fact that a lot of people in the North are liberal and open.”

Another genius director Karen’s collaborated with is Steve McQueen.

“Working with him on Hunger was a film masterclass,” she declares. “Unbeknownst to me, the casting director came to a play I was in at the time and then invited me in for a chat. I spoke to Steve who was fascinated with the history of Belfast and my own experiences of The Troubles. I found him equally fascinating. You can tell when you meet Steve that he’s an artist. He’s also lovely, warm and genuine and managed to create a very positive atmosphere on set, even though the subject was so dark. You thought, ‘I’m part of something really special here’. They rebuilt some of the H Blocks, which two of the actors, Liam and Brian, who were playing Bobby Sands’ right-hand men, went and stayed in overnight. They donned the blankets and everything trying to get a feel for what it must have been like. It’s an incredible film.”

Karen is equally enamoured of the two years she spent as a member of the Vikings cast.

“I did twelve episodes and, wow, the scale of it! Nothing was fake. If they needed a cathedral, they built it with stone floors. The main set was a 360 room with massive candelabras, gold thrones and big heavy doors. I shouldn’t be telling you this but Vikings nerds might like to re-watch the scene where I’m whispering something dark and conspiratorial to Huw Parmenter who plays my brother in the series. Not realising the cameras were rolling, I was saying, ‘So are we going to Nando’s later?’ We got an awful shock when they shouted ‘cut!’ I thought, ‘Oh my God, a lip reader’s going to see it and it’ll get out that we were talking about chicken during a big scene.’ But it didn’t. Until now!”

Cellar Door is on general release now