That its tale of a pious young man’s possession by the apparently physical manifestation of his doppelganger pretty much set the template for every psychological horror yarn since, you can see why. Mark Thomson’s adaptation acknowledges the ongoing fascination with such fare by beginning and ending his production with a pair of contemporary cops exhuming the corpse of Robert Wringham, and his collected and possibly unreliable confessions with it.

What happens in between on Neil Murray’s revolving graveyard set remains faithful to the dark ambiguity of its source, putting flesh on the narrative’s bones without ever over-egging its inherent melodrama. Central to this is the casting of Wringham and Gil-Martin, the devil on Wringham’s shoulder who pushes him into ridding his world of evil with the zeal of a convert. Ryan Fletcher is suitably pale and haunted looking in the role, the polar opposite to Iain Robertson’s flint-eyed Gil-Martin, a character more complex than any temptation to play him as a moustache-twirling villain might suggest. Nor does Thomson overdose the stage with Hammer horror clichés of Victorian gloom and doom, preferring a modern-looking sheen to proceedings.

As Gil-Martin shapeshifts his way into the loveless Wringham’s affections, the big question is did the Devil make Wringham do it, or are the voices in his head his own? Even when Gil-Martin says to Wringham that “I’m so closely bound up with you I feel like we’re the same person,” the answer isn’t clear, and the play is all the better for it.

Star rating: *****