Before saying anything else, let me reassure you that this review is not going to give away whodunit – I’m now officially a partner in crime of The Mousetrap, and therefore sworn to secrecy.

Indeed, there’s something of the sworn-to-secrecy ‘club’ about the whole Mousetrap experience as the show goes out on tour for the first time in its 60-year history. Still playing at St Martin’s Theatre in the West End, the Agatha Christie classic has notched up all kinds of records as the longest-playing theatrical production in the world. Ever.

And while it’s a perfectly serviceable example of the genre, the biggest mystery is not who is causing the death count to rise in the cut-off, snowbound rural guest house that is Monkswell Manor. No, the biggest mystery is why it is still running for 60 years with no sign of letting up.

The fact is there’s nothing outstanding about it. The plot is somewhat creaky and slow, the playing camped up, the dialogue dated and stretching credulity. Money has clearly been spent on the wood-panelled set – but with no ordinary programmes for sale and a hefty eight quid required instead for the souvenir brochure, the audience deserves some return for its investment.

What they get is to be part of the club. The producers should issue badges at the exits: “I’ve seen The Mousetrap.” Because there really is something of a frisson about watching it, however ordinary the actual product is, and being inveigled into the club.

It doesn’t really matter who’s in it – for the record, the cast includes an underused Graham Seed and a curiously miscast Karl Howman – or even whodunit. Perhaps the greatest pleasure of The Mousetrap is to be able to say to the world: I’m now a partner in crime.

MICHAEL DAVIES

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