“I only wish it had been longer.”

That’s how we talk about revelatory art. Creations that move and change us. Things that feel extraordinary and insufficient all at once. It’s also how I’d describe Professor Marston and the Wonder Women – a charming if imperfect biopic that’s the rare film that would have benefited from a longer runtime.

Angela Robinson tells the story of the creator(s) of Wonder Woman: the professor, William Moulton Marston (Luke Evans); his wife, Elizabeth (Rebecca Hall); and their lover, Olive (Bella Heathcoate). Theirs is an expansive story, one that weaves the central trio’s polyamory through the suspicion and discrimination of society while also incorporating psychology, the invention of the lie detector, a hefty helping of bondage and, of course, the inspiration for Wonder Woman herself.

In the film’s best moments, it sings. The central romance, carried by Evans, Heathcoate and especially Hall’s committed performances, is utterly convincing. The film is unapologetically sexy: Evans is raw sexuality, Hall flirtatious, Heathcoate coquettish. The way Robinson’s camera lingers as, say, a golden cord is wrapped around Olive’s body feels frankly radical in the face of prim, polite period biopics (think: The Imitation Game or The Danish Girl).

This sexuality isn’t window-dressing. Professor Marston and the Wonder Women is overtly political, offering everything that such contemporaries promise but fail to deliver. This is a story about unconventional romance, and sex, and kink, and how these things can be – and indeed, should be – revolutionary and controversial. All tied together in this is the conception of Wonder Woman, who is described with unabashed fervour by William as ‘psychological propaganda.’ His comic is intended not just for entertainment, but to teach children the pleasure of ‘submission’ (to a benevolent leader) and the power of women.

The screenplay revels in the symmetry between William, Elizabeth and Olive’s private lives and the superheroics of Diana Prince. The film’s most enjoyable moment is a frenetic montage of kinky Wonder Woman panels – so much bondage – intercut with the trio’s own bedroom experimentation.

Yet Robinson is, perhaps, too enamoured with such parallels. The bulk of the film is awkwardly crosscut between the tale of the trio’s romance and a tense meeting between William and Josette Frank (Connie Briton), chairing a decency panel addressing the comics. This is a well-worn trope that makes for an awkward fit here; we’re treated to uncomfortable explanations of Wonder Woman’s secret identity (as though the panel is entirely unaware of the comic’s contents) as the Marstons set about pretending to be a ‘normal’ family in the suburbs. An occasional underline of the synchronicity between the trio and their creation is understandable, but too often Professor Marston trespasses into overly-obvious territory.

Those without sensitivity to the tiredness of biopic tropes may forgive these flaws. Less forgivable is the rushed pacing of much of the film’s second half. While I understand that a story this broad requires some narrative elision, too many powerful emotional beats as fast forward past by a screenplay that’s just too economical. For example, we cut from Olive announcing she’s pregnant when the trio look to be breaking apart to the three of them living together, any uncertainties apparently smoothed over off-camera.

So – “I only wish it had been longer.” Professor Marston and the Wonder Woman is wonderful when it works. With an extra 20 to 30 minutes to expand its emotional arc – or, perhaps, a tighter focus on a shorter time period – it would have been truly magnificent.