Warning: Agatha Christie’s classic murder mystery, on tour at the Playhouse this week, comes with audience obligations. The secret of whodunnit must remain locked in our hearts. Given that The Mousetrap is the longest-running show in the history of British theatre, I wonder at what critical mass of showgoers this social contract will become irrelevant. There are, I suppose, 65 million people in the UK, and plenty more abroad, so probably best to keep mum for now. Which doesn’t, unfortunately, make it terribly easy to write about.

The plot is as convoluted as our city’s road network, though arguably not as difficult to navigate. It begins, in typical Christie style, with a group of people trapped in a country guest house who discover a murderer in their midst. A policeman arrives and, over the next two hours, attempts to uncover the criminal. Can’t really say much more, but remember: everyone has a backstory; trust no one.

As a huge fan, and someone who has read all her crime novels at least twice, I think Christie’s work is underrated. People often don’t mention her humour, incisive observations about human nature, or ability to fashion belief out of fancy. I’m sure a TV documentary once suggested that her sentence structures stimulate a reader’s brain to release pleasure-inducing hormones much like addictive substances do. Yet what one ultimately finds in these exhilarating, junkie reads is safety: nothing is truly scary (except, perhaps, the ignorance of the upper classes) and, in the end, all flyaway strands are patted into a nice, neat topknot. It’s like a joyride in a Honda.

Tonight’s vibe was not dissimilar: spooky, but my nails survived; light, but not farcical; a few gasp-inducing curve balls; a conclusion as satisfying as pyjamas. I didn’t know how faithful this adaptation was to the original, but some characters seemed less rounded and purposeful than others, and felt at times a little over-acted. However, I particularly enjoyed Anne Kavanagh’s interpretation of crotchety guest Mrs Boyle. The set was beautifully convincing of a formerly-glorious-now-shabby country house on a freezing winter’s day; the staging was traditional. Overall, a super, endorphin-releasing, neuron-tweaking affair.