The Fifth Step may be Jack Lowden’s debut at the Edinburgh International Festival, but he’s no stranger to actual steps. If you’ve enjoyed his performance as River Cartwright in the excellent spy thriller Slow Horses, you’ll know he spends an inordinate amount of time running. More often than not, down steps. ‘A lot of that running is done during night shoots,’ says Lowden, with a look that suggests it’s not without effort. ‘So it’s three in the morning and you’re sprinting again and again, or you’re in some deserted tube station that the production has taken over. And River always runs downstairs, never up; there’s really no cool way to do that. We were just shooting the last series and I turned to the director and said “you get up here and try and run downstairs”. Because your brain has to make a decision: do I do one step quickly after the other, or do I try and skip two or three? It’s a very unnatural thing to do. So hopefully, if we get to do any more series, I’ll be running upstairs.’ 

His turn as MI5 agent Cartwright is just one of a series of TV and film roles Lowden has secured in recent years, building a formidable reputation as one of the UK’s finest actors. Whether he’s playing a Russian count in War & Peace, a young Morrissey in England Is Mine, Lord Darnley in Mary Queen Of Scots, war poet Siegfried Sassoon in Benediction or infamous bank robber Kenneth Noye in The Gold, you can be certain Lowden will draw you in with his charismatic believability. And, chances are, he’ll have mastered a new dialect for it. ‘It’s a constant bugbear of mine,’ says Lowden, when I point out how nice it is to hear him speak in his Scottish accent. ‘I miss acting in my own accent because it’s just one less thing to think about. And I feel like I can get into it, delve a little bit deeper.’

For The Fifth Step, he’s got his wish. Playing alongside Sean Gilder in David Ireland’s new play, Lowden portrays a young Scot meeting up with his Alcoholics Anonymous sponsor. Both actors have been part of the Slow Horses cast, but never at the same time. They did, however, share a scene in The Gold, which turned their mutual admiration for each other up a notch further. ‘I’ve always known Sean’s work,’ says Lowden. ‘He’s just one of those effortless actors. If I go to the cinema or theatre, it’s the actor that makes me want to go. I just love watching brilliant ones be brilliant and Sean has always been one of those. When I found out he was going to be in scenes with me in The Gold, it was quite daunting because he’s so technically brilliant. And then I saw his scenes in Slow Horses, particularly the ones with Gary Oldman, and the pair of them just crackle on screen. I’ve never done a two-hander before, so I just wanted somebody that I knew would, for want of a better word, carry me through.’

It’s unlikely Lowden will need anyone to carry him anywhere, but Gilder’s enthusiasm for working with him on stage is equally matched. Although he too has noticed Lowden’s propensity for swift movement. ‘Jack spends a lot of his time running around on his own in Slow Horses,’ says Gilder with a laugh. ‘He’s a very good runner. But what was lovely about working with him on The Gold was they were kind of two-handed scenes. So even though they were short, we immediately spent some time together without lots of other people around and got on very well. So I was truly excited about The Fifth Step, because the two days that we worked together on The Gold we didn’t stop laughing. There was an immediate click. And I remember going home to my wife and saying “I’ve met this actor today who I just loved and felt so relaxed with, he was just so funny and such fun”. So, when I was approached about doing this play, I thought let’s take those two days of fun that we had and do two months of real fun.’

Gilder’s prolific career on stage and screen has seen him play Paddy Maguire in Shameless, as well as roles in Poldark and Sherwood, and most recently Mary & George and Passenger on TV, and Dear England at the National Theatre in London. When we speak, he and Lowden are in the midst of rehearsals at the National Theatre Of Scotland, and very much enjoying the quick-fire nature of Ireland’s dialogue. ‘I think Jack and I have a similar energy,’ says Gilder. ‘We like to keep the ball in the air, metaphorically. We’re not back-foot actors; we look each other very much in the eye, we’re very direct people. And with David’s script, it’s a bit like two very good tennis players hitting a ball around very quickly into different parts of the court and hoping the other one can get there quick enough to hit it back.’

In a bid to keep some of the mystery surrounding The Fifth Step intact, neither actor is keen to reveal too much of its contents. Those who have tackled the Twelve Steps advocated by Alcoholics Anonymous will know that the fifth one involves admitting to themselves and others the exact nature of their wrong-doings. But according to Gilder, we can expect much more from this exchange between a sponsor and his young sponsee. ‘It’s a very big play, even though it’s a two-hander,’ he says. ‘Its themes are much more than just Alcoholics Anonymous. And I think, without giving too much away, audiences will be taken on a journey of various emotions between these two people. The dialogue is very specific and brilliant but the actual subtext makes it a much bigger play than it may seem when you first start watching it.’ 

With a topic this sensitive, research can prove problematic. AA meetings are notoriously private affairs but fortuitously, for Lowden, his role as producer on new film The Outrun opened some doors. Starring his real-life wife Saoirse Ronan, the story follows author Amy Liptrot’s journey of recovery. ‘That was an enormous help, because on The Outrun we went to approach real AA groups,’ says Lowden. ‘And they ended up being in the film. Not one entire AA group, but people who have been to AA meetings and felt comfortable sharing their stories. And it was one of my favourite things from that shoot, watching these people and seeing how involved in their stories they could become at the drop of a hat. Because I think what AA also does for many people is develop wonderful orators and storytellers. And every single story they tell is just laden with humour.’

Despite his film and television accolades, Lowden cites theatre as his first love, having spent much of his early career on stage (including a memorable performance in the National Theatre Of Scotland’s production of Black Watch). But The Fifth Step in particular is cause for excitement. Growing up in the Scottish Borders, and living in Edinburgh for a number of years, he has been a regular visitor to the city’s festivals. But this will be his first time there as a performer. ‘I’ve never done anything at either the Fringe or the International Festival,’ says Lowden. ‘But I’ve gone to them since I was very young, so August has always been associated with standing about in beer gardens and running between things. So to be in a play is kind of bizarre, and I’m really excited that I’m doing it in a year when Nicola Benedetti is running the whole shebang. I love that it’s somebody of her age doing it; it just feels a lot more urgent and fun. She’s a phenomenal ambassador for the arts in this country, so it’s a big honour to be there.’

The Fifth Step, Lyceum Theatre, 21–25 August, times vary; main picture: Simon Murphy.