Colin and Charlotte lead the perfect suburban life – a life which their neighbours, Ben and Hannah, would love to live too. And then, one day, the privileged pair reveal their secret: an unusual home improvement, ancient symbols painted on the attic walls, which they claim have the power to realise their most cherished wishes. Ben is intrigued enough to paint his own symbols, and stitch curious designs into the lining of his coat. They give him confidence, he says – help him to be the best version of himself. So where’s the harm in that?

On one level, Sycamore Grove is a study in addiction: how something which starts as a harmless pick-me-up can become a worrying crutch, then a self-destructive necessity. But on another, it’s an occult horror, as we quickly discover that the symbols truly do have a dark and primal power. How that power changes Ben – and how it’s already corrupted Colin and Charlotte – is the intriguing centre of Daniel Williams’ script.

The relationship between the two couples is nicely observed. Colin and Charlotte are masters of one-upmanship – often comically so – and, while Ben and Hannah aren’t naturally competitive, nor are they strong enough to escape being dragged in. In a clever and unsettling choice from director Liam Rees, the alpha pair sit silently on the periphery of scenes they’re not in, with actor Nicholas Alban capturing Colin’s fixed expression of condescending superiority particularly well.

The pace of the storytelling is a little uneven, however. The paranormal theme’s exposed very early, with no time allowed for gnawing suspicion, and the conclusion – though legitimately a shock – feels snatched-at, too. Since the play currently runs at 10 minutes under its advertised hour, there’s room to linger more, to let the audience guess at horrible truths before they’re confirmed or dispelled. Conversely, scenes between Ben and Hannah dragged after a while, as the parameters of their dispute are set early on and don’t evolve much from there.

But the power and nature of the mysterious symbols is revealed with satisfying menace, while a creepy, scratchy soundtrack is sparingly but effectively deployed. One crux scene is genuinely spine-tingling, as the lordly Colin crumbles into panic at the force that might have been released – and while the seeds for the denouement are fairly planted, the outcome still comes as a surprise. So there’s still some room for Sycamore Grove to grow but, for now, it’s an interesting and well-staged horror.