The programme notes describe Mark MacNicol’s Serve Cold as a “cracking wee script” – and I think I’d have to agree. When two women – one a prostitute, the other a doctor – meet one night on a bridge in Glasgow, a chain of events is set in motion that only one of them could have foreseen… and it’s not necessarily the one we might expect. Darkly humorous and unapologetically twisted, Serve Cold makes us question our assumptions and reflect on the lengths some people, even those we think of as “respectable”, will go to in the name of revenge.

Concerned that Joy (Paula Gilmour) is about to throw herself in the river, Grace (Anna Marie Burslem) stops to try and talk her out of it. The two end up back in the attic that Joy calls home, where events take an unexpected turn as she reveals calmly that she’s been stalking her ex-boyfriend in a variety of unpleasant and twisted ways. Tonight is the grand finale – if Grace is willing to do her part, that is.

MacNicol’s storyline at times strains credulity a bit, but PJ Stanley’s production is consistently excellent. Serve Cold is driven by its characters, and the performances from Anna Marie Burslem and Paula Gilmour are right on the money. Grace has every reason to be mad at the world, but her innocent, almost childlike determination to see the positives in everything and everyone around her means she’s the one we instantly warm to and root for throughout the play. She has no filter; she says what she thinks and doesn’t try to hide her growing discomfort (which matches our own) as the evening progresses and humour turns to horror.

In contrast, Joy is the picture of calm professionalism – alarmingly, even when discussing in detail all the shocking things she’s done to her ex – and displays a truly psychopathic lack of remorse. It’s chilling to reflect that this is a woman countless people entrust their lives to every day – people who would probably turn their backs on someone like Grace if they saw her in the street. It’s testament to Paula Gilmour’s performance, however, that we find ourselves unable to hate Joy completely; every now and then we catch a small glimmer of humanity behind the mask, and the play’s conclusion is actually oddly heartwarming – albeit in an extremely dark and messed up way.

It’s not only in personality that the two women are worlds apart; a recurring theme of religion (their names are, I suspect, no accident) looks at two very different ideologies when it comes to retribution. While Grace lives in constant fear of going to “the bad fire”, a hangover from her evangelical Christian upbringing, Joy is a great believer in doling out more earthly punishments – ironically, by subscribing to the biblical principle of an eye for an eye.

Though its short two-day run at the appropriately atmospheric Katzpace is already at an end, Serve Cold is the kind of play that’s not that easy to forget. Gripping and disturbing, it boasts two fantastic performances and provides a good amount of food for thought – but more importantly, it makes you think long and hard about going anywhere near the attic any time soon.