Maybe the reason it’s taken 15 years for Adam Guettel’s multiple Tony award-winning show to make it to London is because it’s so bloody hard to perform.

So kudos to former English National Opera director John Berry and partner Anthony Lilley for bringing it to the UK in their first production for new company Scenario Two. It isn’t a perfect production, but they’ve put together a crack team: opera stalwart Renée Fleming, young megastar Dove Cameron, stage legends Alex Jennings and Malcolm Sinclair, fresh talent in Rob Houchen – all in the service of Guettel’s sweeping music.

It’s hard to define his style. It’s strange and restive, with luscious strings like a Morricone film score. Keys never settle, and melodies dart in every direction. These aren’t tunes you’ll be humming out of the door, but the cumulative effect is one of sumptuousness and great romance.

This gift of a score is wrapped around a pretty basic book full of crass Americans and impassioned Italians played for laughs; it borders on Dolmio advert territory at times.

Everything in Daniel Evans’ production feeds into a picture of elegant, romantic Florence: the crumbling stone walls, the shrines and shutters, Fleming’s drop dead gorgeous gowns, which change at a rate of knots.

Yet the monolithic and unchanging presence of Richard Jones’ circular set brings something inert to the production too, which even Evans’ graceful direction can’t quite eradicate. The vastness of the Royal Festival Hall saps some of the show’s vitality and energy.

Fleming plays Margaret Johnson, holidaying in Florence with her young daughter Clara. Clara meets dashing Fabrizio, and they fall in love. But Clara has difficulties with her emotional and mental development. Craig Lucas’ book is surprisingly acute about her mental capacity – the question of whether Clara can make decisions for herself – even if this gets swallowed up in the comic dreck.

Fleming’s still got it – her solos are sublime and her elegance palpable – but there’s good stuff from Dove Cameron’s Clara too. Her voice is clearly up to the tricky melodies, and she’s a charming performer, even if a broad smile is about the beginning and the end of her expressiveness. Playing a character with learning difficulties, Cameron’s performance is sensitive even when the production around her slips into pastiche.

The standout performance, though, comes not from Fleming, Cameron or Jennings but Rob Houchen – his blow-away presence fills the piazza. He’s adorably earnest as Fabrizio, a young romantic full of the first flush of love. And his voice is something else; whether it’s a whisper or a belt, it hits every note of the unsettled score to perfection.