They were both married, so it was just a brief affair in the Mexican summer of 1937 between the political revolutionary, Leon Trotsky​, 57, and the artistic revolutionary, Frida​ Kahlo​, 29. "What," asks the eccentric musical Carmen Live or Dead, "if that affair had resulted in a love child?" Natalie Gamsu​ is Carmen Frida​ Leon Davidovich​: hermaphrodite, fugitive and seeker of a foreign emotion called love.

The show, with book by Craig Harwood and music and lyrics by iOTA, initially lives up to all the enchantment of that premise (conceived by Harwood and Gamsu​). You have a deliciously disorienting feeling of having fallen into someone else's dream; one that could go anywhere at any moment; one made vibrant with all the most daring colours of theatre, visuals and music; one that might just be a little bit dangerous.

Dann​ Barber's magical set references Kahlo's​ art, and Gamsu​ (in a costume by Shauna​ Lovisetto​) looks like she has just stepped out of one of those paintings, as do Andrew Kroenert​ and Stefanie​ Jones as the cadaverous Angel and Delilah. The latter pair are essentially mimed roles in a one-woman show, with Kroenert​ primarily musical director (playing acoustic guitar and piano) and Jones adding violin.

Kahlo's​ art uniquely fused a deeply personal mysticism with emotional devastation, and the show leavens that intensity with humour that is variously ribald, vaudevillian and very black. iOTA's songs sustain the anything-could-happen edginess, with the closing The Great Divide conjuring a performance from Gamsu​ that impales us on a fathomless sadness.

What a tragedy, then, that Carmen Live or Dead is not as consistently brilliant as its beautifully oneiric​ touches; as its flaring outrageousness and larger-than-life performances, with Gamsu​ cutting a swathe through every word. Despite being capable of setting the bar so high, Harwood intermittently lets the quality fall away. Lame jokes are allowed to intrude on a show that should be relentlessly clever; silliness allowed to substitute for surrealism. Even the exquisite character of Delilah is made to break her own spell by speaking!

Now is not the time for Harwood, iOTA, director Shaun Rennie and the rest to accept "almost right". Now is the time to be dissatisfied and ruthless: to turn the entertaining into the consistently sensational. It's so close to being that – including boasting the best and softest sound I've ever heard in the Hayes.

Until May 6