Part of the job of writing about films is to stress-test received wisdom. (Viz. my colleague Nigel Andrews’ deathless review of Cats.) Sometimes, though, the consensus has it covered. So it proves with Music, the already notorious film-making debut of star songwriter Sia. That part of her reputation survives. The film features several of her tunes, all with the bright machine melancholy of the best modern pop. The movie itself is a catastrophe, the product of many poor decisions and one spectacular act of hubris.

To address that first: Music is the name of the apparent heroine, a 16-year-old girl with severe autism. She is played by the neurotypical Maddie Ziegler, whose casting caused instant alarm in the disabled community. “Nothing about us without us” is the modern benchmark and rightly so. But it should still be possible for an able-bodied actor to play a disabled character with insight and sensitivity. These are not traits of this performance. The result is genuinely hard to watch — mimicry that feels like mockery. Yet the real fault lies with a director whose lack of serious research into autism itself became infamous long before the film’s release, and which screams from every scene. “Springtime for Hitler” had nothing on this.

In all fairness, the film is bad on many other levels too. Not least is the fact that characters with autism only exist at all — so it turns out — to be props in cloying stories about the self-discovery of their troubled older sisters. (That sister is Zu — yep — played by Kate Hudson as a narcissistic flake who just might find redemption caring for Music.) How nobody involved in this doomed fiasco simply said no at any — or every — stage is baffling. Fortunately, you can.

★☆☆☆☆

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