It’s always a good sign when the Royal is virtually full on a Wednesday night. The 39 Steps has been packing them in at the Criterion Theatre for at least six years now, and if the reaction from the audience in the Royal is anything to go by, there’s no reason it shouldn’t carry on indefinitely.

I’ve not read John Buchan’s original book – or indeed seen the film – but I would guess Patrick Barlow’s adaptation (he of the National Theatre of Brent) is an extremely loose one. It’s a 1930s spy story – our hero John Hannay has to save the country by preventing the secret of the 39 Steps from leaving our shores. Unfortunately, he doesn’t know what the secret is – and he is followed the length and breadth of the country by the police who think he has committed murder – but he hasn’t. And if the police arrest him and get in the way of his trying to save the nation, well, dash it all, it wouldn’t be worth thinking about, would it? And that’s just the start. It’s a maniacally silly set up, beautifully lampooning the styles of the era and the whole “B” movie syndrome; and it’s interspersed with some wonderful accents – stiff upper lip British, over-the-top faux Scottish, and Marlene-Dietrich-German. By the way, all four actors speak with impeccable clarity – not a word is garbled, which is something I always appreciate. And it’s all very funny.

The talented cast of four play 139 roles apparently! The way they interchange is extraordinary. In some scenes they actually swap roles with each other as the scene progresses, which is hysterical. The whole pace of the show is amazing; it’s really fast and full on, gathering an exciting momentum all the time, and all the cast work together seamlessly like a well-oiled machine. They also recreate a variety of sets and locations with just a handful of props – a few suitcases, a door, a window frame, a very jolly toy train and with the help of a very lively lighting and sound plot.

Richard Ede plays Richard Hannay and he’s brilliant for the role. He’s suave and sophisticated, but not too much – so that he can still have the Mickey taken out of him. He’s full of derring-do and heroic charm, which makes it all the funnier when he gets into ludicrous scrapes from which he inevitably bounces back. Both Mrs Chrisparkle and I thought he gave a funnier and more convincing performance than the actor we saw play the part in the West End a few years ago.

Charlotte Peters is also great playing all the female roles, from the alluring Germanic vamp of Annabella Schmidt to the not-so-timid-after-all wife of the austerely religious Scottish crofter; and of course she is directly involved with the happy ending. You wouldn’t expect it not to have a happy ending, would you? The rest of the cast are played by Tony Bell and Gary Mackay and they dovetail perfectly with each other. I can’t go in to too much detail about these performances because it is the inventive nature of the play and the way it is staged that provides all the entertainment – and you wouldn’t want me to spoil it for you. But I loved the train scenes, the Mister Memory scenes (am I right, sir?) and the Scottish hoteliers.

Huge fun, lashings of tongue-in-cheek, and a superb ensemble performance. It’s touring the whole country until July, so if you can’t get to London, this show can come to you. The whole audience were in stitches all night. Highly recommended.