United Kingdom: Pacific Island of Saint John, a British Overseas Territory, Where a Scottish Researcher Named Kerris Arrives to Study Plant

Welcomed by Joe, a former merchant seaman played by Xander Cowan, she senses something amiss in nightly church services led by an elusive figure called the prophet. Directed by Fraser Scott, the well-acted production starts promisingly, hinting at a cover-up behind the slow-moving administrative machinery of this faraway British remnant and an out-of-control cult following a rewritten Bible. However, as the drama unfolds, it feels like the real story lies elsewhere: Kerris has a personal interest in charismatic religious leaders, but her backstory is hazy and slow to reveal itself, leaving audiences at one remove from the action.

The result is an uncontroversial message that cults are bad, with only a shallow perspective on why such conviction attracts followers. At Assembly Roxy, Edinburgh, until 31 August. a mysterious tale of faith at the end of the world.

A researcher encounters an isolated community in thrall to a mysterious religious leader in Jack MacGregor's atmospheric but elusive drama. What impresses about MacGregor as a playwright is their willingness to take us into the wider world: Nightlands was set in a deserted Russian research base in Svalbard; Everything Under the Sun concerned militias in Mali; and Our Brother played out in Cambodia under Pol Pot. So it is with Prophets, which begins with Kerris's arrival on the sparsely populated island of Saint John.

Her job is about the dawn of time, but the locals are readying themselves for the end of days. All this starts promisingly in the well-acted production directed by Fraser Scott. MacGregor's political sense suggests there could be some kind of cover-up going on behind the slow-moving administrative machinery of this faraway remnant of the British empire, compounding the impression of an out-of-control cult taking its lead from a rewritten Bible.

But as Prophets plays out, it increasingly feels as if the real drama is somewhere else. Kerris, it transpires, has a personal interest in charismatic religious leaders, but her backstory is hazy and slow to reveal itself. We get too fleeting an insight into whatever trauma she went through in Scotland.

And for as long as she is outside the cult looking in, we feel at one remove from the action on the island. It means we are left with the uncontroversial message that cults are a bad thing, and get only a shallow perspective on the social forces that make such religious conviction attractive in the first place. All our Edinburgh festival reviews.