‘On the set, I showed people a picture of Lorn in his Bridgerton costume; they just couldn’t believe it was the same guy,’ says Ciaran Lyons, writer-director of Tummy Monster, a psychological thriller/dark comedy which launches at Glasgow Film Festival. Making the jump from costume drama to playing a tattoo artist under pressure from a threatening pop star is quite a reversal. Macdonald plays the stressed-out parlour owner who enters into a dangerous mind game when unexpectedly trapped in his shop with a sinister international pop star, played by Orlando Norman.

‘Orlando came in with such great energy; we originally imagined his character as a kind of grungier Justin Bieber,’ says Lyons, making his feature debut after helming a series of videos for acclaimed Glasgow-based studio Forest Of Black. ‘There are a few Bieberisms in there, but we were also thinking about someone like Post Malone, and what the psychological process is with someone who has that kind of public persona. Orlando gave us that.’

‘The shoot was so intense,’ says Macdonald. ‘Me and Orlando were actually living in an Airbnb and spent a week together in there. It felt like we got really, really close; it was like going home with your enemy each night. The two men are so different. I’m Tails, a tortured artist; his tattoos are his art, they mean everything to him. Tummy is at the highest point of his career, and he just goes with his instinct about things. There was a real sense of intensity and risk while we were shooting. I’d compare it to Andy Murray in the fifth set, grinding one out; he may look miserable, but he’s loving it, and so did I. It’s my Nic Cage performance.’

With cinematic antecedents in the two-man psychological warfare of Jonathan Glazer’s Sexy Beast, and also the transformative competitive bromance of David Fincher’s Fight Club, Tummy Monster’s action sees the men try and wear each other’s resistance down. A vigorous five-day shoot in the East End of Glasgow provided the setting for a showdown between two artists. ‘I try not to tell people how much the film cost or how long it took to shoot until after they’ve seen it; there are pre-conceptions people have of small budgets,’ says Lyons. ‘We shot largely on one location and wanted it to be claustrophobic, but also colourful and constantly moving. Shooting on an Easter weekend in Glasgow with a karaoke party going on next door and a Celtic-Rangers match playing at the same time just added to the overall intensity.’

Tummy Monster gets its world premiere at Glasgow Film Festival, and Lyons hopes his film can go on a festival run and get seen outside of Scotland; he’d love to make another small-budget film, but not back to back with this one. And for Macdonald, it’s time to sit back and enjoy this film, taking a break from the pressure of playing a character on the edge. ‘I was thinking about Tummy Monster the other day while watching Breaking Bad. It’s also got a real dark-comedy feel, because you’re watching someone making such bad decisions, and having to deal with the consequences. Hopefully people will get that same kind of feeling from watching Tummy Monster.’

Tummy Monster, GFT, Glasgow, Saturday 2 & Sunday 3, Thursday 7 March, as part of Glasgow Film Festival.