If you’re penning a locked-room murder mystery, why not set it in the most frequently-locked room of all? Slash is a detective story set in a toilet – specifically, the men’s toilets at a high-school reunion. The title, the publicity and the rather impressive set all lean into that minor taboo, but don’t go if you’re looking for juvenile humour: on the contrary, playwright Huw Turnbull and director Minnie Cross deliver a show that’s often hilarious, but clever and sophisticated too.

A 50-minute show clearly can’t offer the most complex of plots, but we genuinely do get a compact fair-play mystery. If you watch and listen carefully, you have every chance to figure out whodunit… and though I was scratching my head over motive as I left the theatre, I think I’d worked it out by the time I reached the Royal Mile. The set-up precludes a traditional drawing-room denouement, but the script would still benefit from a little exposition at the close – to spell out for those who’ve missed it not just what happened, but why.

The whole play, in fact, both demands and rewards your attention, as there’s constant comedy in half-suppressed remarks and quirky moves. In contrast, there’s little subtlety to the characterisation – but it’s absolutely none the worse for that. Gordon Stackhouse has the most fun as bit-part actor Tom, with an overblown thespian demeanour and constantly-drifting accent, while Leo Odgers’ expressive face and clownish physicality bring the less-than-competent GP Danny vividly to life. Ruth Maley’s character Billie is there to hold it all together, and she too strikes a fine balance between reason and alarm as the storyline begins to unravel around her.

Any classic mystery needs a detective. Here, the role’s filled by mysterious newcomer Alex, whose reasons for being in the bathroom haul us from detection’s golden era right into the present day. Charlie Mitchell brings us a memorable pastiche of many a TV cop show as he plots out the details of the murder, albeit that he’s sometimes hilariously oblivious to clues the rest of us can clearly see.

It’s not played completely for laughs – there is (of course) a secret buried in the past, which is handled with the weight and awe it deserves – but overall this is a fast-paced and accomplished character comedy, which happens to be a well-plotted mystery too. Fans of the genre will admire how it brings well-loved tropes to the most unlikely of settings, while everyone can enjoy the sharp one-liners and crisp physical humour. Worth spending a few pennies on.