Oh, the tragedy of Vote Macbeth! Destined for greatness, yet betrayed by a fatal flaw. This ambitious new musical by John Paul Liddle has all the ingredients of a smash-hit success, but – at least on the night I saw it – was badly failed by its execution.

The concept is brilliant – a natural updating of the classic plot, very much matched to the zeitgeist. We’re in a near-future, presumably independent Scotland, where Duncan isn’t a king but a president. Macbeth is his veep, Banquo’s an overlooked junior, and the Three Witches are a gaggle of journalists (who also form the chorus). But the political metaphor isn’t stretched too far: Macbeth still literally murders Duncan, lending the plot the gravity and consequence it needs. As a self-confessed Macbeth geek I simply loved all this, and was continually delighted by how cleverly they referenced the famous plot twists and soliloquies.

Liddle’s original score, orchestrated by Lorna Bailey, is fantastic too. The pop-musical style is comfortably familiar without being derivative, and there’s a neat recurring Morse-code motif which is oh-so evocative of the TV-news milieu. The lyrics, meanwhile, are intelligent and often audacious, while the obligatory character-defining solos do offer some genuine insights into Shakespearean thoughts and motivations. It’s a humorous and knowing adaptation, but in its own way it’s a thoughtful one.

The plot diverges from the original towards the end and, while the ensuing audience interaction is fun, having Macbeth usurped by a democratic process is arguably missing the point. And I didn’t quite understand why Fleance – who’s an adult in this version – was wearing glittery high-heeled boots, until someone explained afterwards it was an homage to Beyoncé. This is all fine, though. It’s a musical. That kind of thing is allowed to happen.

But there’s one thing that wasn’t fine. And there’s no way of softening this, so I’ll just come out and say it: on the night I attended, it sounded terrible. The cast have an impressive background in musical theatre, so I have to assume they can sing in tune, but the fact remains that – with a few honourable exceptions – they didn’t.

The show I saw was defined by cacophonous duets and screeching solos, all performed in competition with an overly-loud backing track. And the choreography, while present and correct, didn’t do much to lift or energise the piece. I had to wonder why this Scottish production of a Scottish story didn’t find room to strip a willow or two.

It’s such a shame, and I harbour hopes that I simply went on a bad night. The book, lyrics and score are worthy of greatness – I truly mean that – and it isn’t hard to imagine it succeeding on a much larger stage. Alas, though. It may beget a 5-star triumph, but it be none.