Making a bet with the devil rarely turns out well. But James Napier, the protagonist of this gently haunting one-man show, has reason to believe he can buck the odds: for he carries a secret, a secret he dared believe would give him the upper hand on Old Nick himself. Needless to say, he should have been more careful what he wished for. Today, he's here to tell us how he won his gamble, and then how it all went wrong.

Actor Daniel Hird cuts a louche but dapper figure, his jacket and slacks in stark contrast to the ruff-collared man in a portrait on the table. The reason for the modern dress emerges later on – just one of the carefully-paced plot points dropped in by playwright Jen McGregor. But we learn straight away that the portrait's of John Napier, the famous sixteenth-century mathematician, and that the man who stands in front of us is his brother.

Hird plays James with a hint of wildness, a reckless spirit which piques interest in his character while also providing the foundation for McGregor's clever plot. The early scenes are set in Edinburgh – and since that happens to be my hometown, I can tell you there's plenty of local colour to enjoy. But before long, James's horizons broaden, and Hird's portrayal grows more poignant and desperate as the consequences of his apparent triumph gradually become plain.

James is a gambler, adept with cards and dice; and Hird takes risks too, recruiting members of the audience to play other characters in the story. These crowd interactions are fun and good-spirited, but they could do with being more tightly controlled. It wasn't always clear exactly what Hird expected of the people he brought up on stage – and on the day I attended, there were a couple of awkward moments, as his selected helpers filled the gap with unhelpful improvisation.

And though the plot's tightly-woven, there's one thing that puzzles me: I'm not sure what it has to do with John Napier. We're told that James is the mathematician's brother, but that fact has minimal bearing on the storyline. It doesn't matter all that much – and I suppose the historical connection worked as a hook to get me through the door – but I'm still left wondering if there's some clever allusion here which I didn't quite understand.

What I do know, though, is that this is an intriguing and intelligent play, and that Hird's personable performance belies an undertone of creeping horror. The last few minutes will stick long in my memory, as the full reality of James's gift-turned-curse is finally driven home. There's room yet for a little tightness and refinement – but I'll wager that Old Bones has a long and successful life to come.