I'll admit upfront that I go into this one blind, having no idea the play is based on a cult film of the same name. That turns out to be entirely beside the point, because what unfolds on stage stands perfectly well on its own. A word of warning, though: this isn't a show for everyone. If you'd rather not have your assumptions poked and prodded, you may want to give this one a miss.

The premise is deceptively simple. At a low-key leaving do, academic John Oldman drops a rather extraordinary claim on his colleagues: he isn't quite what he seems, and has in fact been walking the earth for some fourteen thousand years. What follows is a gripping seventy-five minutes built around eight sharp minds picking apart questions of history, belief and identity — turning over what it might mean if someone, through some quirk of biology, simply stopped ageing. Could a person alive today really have witnessed the sweep of human history first-hand? It's a wonderful setup, and the ensemble of characters thrown into the room together makes for a brilliant dynamic.

There's no getting around the fact that this is a play carried entirely by conversation. No flashbacks, no staged action, nothing beyond a room and the people in it talking. That's a considerable gamble for any production, since the dialogue has to do absolutely all the heavy lifting — and here, it does. The cast handle the material with real skill, and I find myself leaning forward, genuinely hanging on every exchange, hungry for the next revelation. The staging itself is stripped back and unfussy, but that restraint works in its favour, letting the ideas take centre stage.

Oliver Franks makes for a thoroughly believable and quietly enigmatic John, holding the emotional centre of the piece with real composure. Around him, Ker Milan, Nick Rumsby, Cici Clarke, Becca Watson, Kieran Dooner, Freddie Elcock and Bridget Benstead all pull their weight, and together the ensemble does a superb job of sustaining that uneasy, simmering tension that runs through the whole evening.

All told, a thoughtful, dialogue-driven piece that trusts its audience to keep up — and rewards them handsomely for doing so, in a tight seventy-five minutes that never once drags.