Inspired by a true story – well, a BBC Three documentary – Everybody's Talking About Jamie follows a 16 year-old County Durham schoolboy with ambitions to become a drag queen. Sat at the back of class in pink socks, idly flicking through a fashion mag, Jamie Campbell's a dreamer through and through. How his careers test chucked up forklift truck driver is anyone's guess.

With The Feeling's lead-singer Dan Gillespie Sells providing fizzy pop for all, this sparky new musical charts Jamie's first shaky, stiletto-heeled steps, but what looks like a staple self-discovery story – a Billy Elliot for the Brexit generation – gradually gives way to something else.

Tom MacRae's book tricks you with tropes, then twists out of shape. Far from realising his dreams, Jamie's is an Icarus tale. His singularity and school corridor celebrity goes to his head. He's blessed with the sort of defiance that defends its right to difference. "Sometimes you've got to grab life by the balls," he pronounces. "You take those balls and tuck 'em between your legs".

In his immaturity, however, that tips into outright affront and when Jamie loses your sympathy, it migrates elsewhere – to softer, supportive characters: his mentor Hugo (Charles Dale), the former drag artist who gives him the push (and the padding) he needs; his BFF Pritti (Lucie Shorthouse), a studious Muslim girl striving to be a doctor; and, most of all, his hard-up single mum, Margaret (Josie Walker).

Gillespie Sells' score is a bona fide toe-tapper, but it's so crowd-pleasing it hurts. His songs, peppy as anything in Bruno Mars' back catalogue, have beats that get right into your bones. The problem, at least early on, is that they're built like chart hits, not musical numbers. A first half full of up-tempo choons – the Kyliesque "Wall in My Head" or the clubbably anthemic "Work of Art" – wears itself out: incidental songs stuck to a predictable plot. Only Kate Prince's S Club choreography really benefits. Jonathan Butterell's staging risks coming across as High School Musical in heels.

How that changes after the interval as book and score both mature. "At Sixteen" criss-crosses youth's lust for life with a lament for its loss later in life. "It Means Beautiful" is a hymn to modest integrity that offsets Jamie's brash confidence with best friend Pritti's quiet brilliance, then comes "He's My Boy", a bracing torch song crammed full of motherly love. Walker belts it straight at the lump in your throat. Every number finds its emotional connection, and a superficial story fills up with rich sentiment.

Deep down, it's a study of the species of pride. Jamie's might be overt, even OTT, but it becomes increasingly obvious how much that costs, even now. Pritti's diligence deserves just as many whoops as Jamie's defiance, not least in her determined decision to wear a hijab despite the abuse she incurs, and Margaret's maternal pride, not just in her son, but through her sacrifices and her resilience, might merit even more. This should be her show. She lets her son take centre stage.

It's not an opportunity John McCrea passes up. He's got more sass than RuPaul series four, and if Jamie takes to drag like a duck takes to water, he's also reckless, vain and presumptuous. Infuriating, in other words, and McCrea lets us come awfully close to giving up on him, only to rein him in. His epiphany isn't self-discovery, it's restraint and, when it comes, that's quite touching. Just as it is when Shorthouse's Pritti finds her voice – and what a voice – or when Walker looks on at her son. Everyone's talking about Jamie. We should spare a thought for those around him.

Everybody's Talking About Jamie runs at Sheffield Crucible until 25 February.

Watch our video in rehearsals with Everybody's Talking About Jamie