ABSTRUSE politeness is a peculiarly English characteristic. You don’t want to be rude; you don’t want to offend people … The tangle you can get in, when trying not to say something possibly hostile (but necessary) can get you into much deeper water, entangle you in ever-more convoluted rigmaroles.

That, in essence, is the backbone of Steven Moffat’s very funny 2022 Chichester Festival play, The Unfriend. Moffat – the Scottish scriptwriter who famously co-wrote Sherlock with Mark Gatiss – took a scenario that is familiar to many of us, and pulled off a masterpiece of farce-cum-didshedoit?

Peter (Mark Payne) and Debbie (Sarah Nias) are a rather scratchy middle-class couple enjoying a cruise away from their annoying teenage children. They have met a flamboyant American woman, Elsa (Liz Stallard) and have formed one of those holiday friendships that normally end after passport control, even when you have exchanged addresses or emails.

But Elsa does follow up, and polite Debbie has replied to Elsa’s emails. Now Elsa is coming to stay, because … how could Debbie and Peter say no?

But Debbie makes a very pragmatic 21st century move – she Googles Elsa. And what she finds rings some very loud alarm bells. Elsa appears to be a serial-killer, who has poisoned various husbands, relations and other people. Debbie wants to cancel Elsa’s visit. Peter, a dithering prevaricator who masks his incompetence in a flurry of indecision and emails, thinks they shouldn’t rush into anything.

And then Elsa arrives – several days earlier than expected. And within a very short time, she is changing their lives – grumpy, gaming-addicted Alex (Dudley King) is outside running and cycling, Rosie (Mabel Hodgson), who thinks nobody takes any notice of her, finds that life is better if you demonstrate understanding and affection … the fractured family members start to actually see each other and enjoy being together.

But … surely Elsa is a killer? So when a policeman (David Hallett) arrives in the kitchen, needing urgent “relief” after being stuffed with Elsa’s sandwiches, the scene is set for one of the most wince-inducing, laugh-out-loud scenes in any recent farce.

It is a really funny play and like all the best farces, just one step beyond everyday experience. The mainly very experienced cast members, directed with skill and perfect pace by Sarah Ambrose, capture the all-too-credible humour of the story, tinged with a frisson of horror. Congratulations to first time Swan actors Mabel and Dudley who bring the teenagers to totally convincing life.

The final character in this comedy of everyday suburban life is the boring neighbour from hell, a man whose ghastly excessive politeness – “You’re a busy man, Peter” – is equalled only by his mundane obsessions, in this case over a collapsing garden wall. Last seen as a five-star US general in the brilliant Swan production of Pressure, Robert Graydon displays his familiar versatility as a man whom you could honestly kill – if you had the means …

The Unfriend is at the Swan Theatre until Saturday 23rd May.

FAC