Bored to sobs, the expat Canadian Richard Hannay yearns for something to distract him from grey London skies and prophecies of war. Something peppy and utterly pointless.

“I know!” he exclaims. “I’ll go to the theatre!”

And so he does – but he gets more than he bargains for in Patrick Barlow’s inventive riff on Alfred Hitchcock’s 1935 film and the John Buchan novel that inspired it.

Instead of a quiet evening in a comfy seat, Hannay (played here by Ian Stenlake) finds himself fingered for the murder of a mysterious Mata Hari-type, chased across the Scottish Highlands and embroiled in a plot to leak state secrets to dastardly agents of the Nazi regime.

Ian Stenlake, David Collins and Shane Dundas in The 39 Steps. Photo © Cameron Grant

Barlow’s The 39 Steps has always traded on its improbability: that four actors can play 130 characters, spin a complex yarn of cross and double-cross, and make us care for the plight of its hero.

All it needs to work (as it did conclusively in 2008, when I last saw it) is actorly skill, precision and the bare minimum of props and set. You can...