Poetry, Lee Chang-dong, 139 mins (12A)

In a novel for the screen, a woman's luck goes from bad to verse

It's a principle of the hard-nosed movie business that it should be possible to sum up any film in an audience-grabbing pitch of 25 words or less.

Try this capsule of South Korean drama Poetry. An elderly woman, worried about her grandson and facing the onset of Alzheimer's, finds solace in attending poetry classes. There you have the new feature by acclaimed writer-director Lee Chang-dong – but I suspect that description hasn't made you think this film might be a rip-roaring alternative to the last Harry Potter.

The fact is, some films barely bear describing, certainly not in capsule form. To adequately evoke a film this subtle and adult, you'd probably have to write it up as a novel. And a novel is what Poetry most resembles. South Korean cinema may be notorious for cultivating extremity, as in the films of revenge specialist Park Chan-wook (Oldboy). But it also has a less sensational rep for nuanced psychological realism, which is Lee Chang-dong's forte – though there's more than a dash of emotional cruelty under Poetry's calm surface. That's evident in the opening: images of a flowing river, with children playing on its banks, before a corpse bobs into view.

We don't find out for a while what's happened to the dead girl – first we meet Yang Mija (Yun Jung-hee), an elderly woman visiting the doctor because she's started to forget words. Soon after, we learn that the girl killed herself because of events at her school – and that Mija's chronically sullen teenage grandson Wook (Lee David) – is one of the boys who drove her to it. Mija is enlisted into a conspiracy of parents who plan to pay hush money to the girl's mother.

But Mija is increasingly preoccupied by the poetry class she's joined. She'll suddenly wander off to contemplate an apricot, or baffle neighbours by gazing up into a tree – "to listen to its thought". All this could be horribly whimsical – and the film certainly plays on the precious tendencies of a woman whose unschooled view of poetry is on the vaporous side. But Mija's distraction takes on a really troubling edge when, entrusted with a very delicate mission, she lets her mind wander to the glory of nature – then suddenly realises that she's blown it terribly.

The horrific story of the dead girl could have provided the sole content for a different film; what's remarkable here is that writer-director Lee focuses so much on the apparent side issue of the poetry class. Without his ever stating the case, it becomes clear that this is a last opportunity for Mija to retain some grip on language, and on her mind. I'm not sure exactly what Lee's take on poetry is, and how it relates to Korean tradition; but I suspect that on the one hand he's taking the idea of poetry very seriously, while being rather wry about certain more airy-fairy attitudes to the discipline.

At a poetry evening, one man intones, "As the stem of last summer's forget-me-not falls from my fingertips" – and I suspect it's as dopey in Korean as it is in the subtitles. Closer to the bone is the tubby gent resembling a South-east Asian version of John Prescott, who turns out to have an effortlessly charismatic way with salty innuendo – to the horror of Mija, who thinks that poetry should be all beauty and nothing but.

But Lee Chang-dong shows that the poetry of cinema can be about the more painful things. A brilliantly uncomfortable subplot involves Mija's work as carer to an elderly man who's had a stroke. One day, he makes an unabashed pass at her; later, in a scene that's dramatically but subtly taboo-breaking, Mija makes her own decision on how to deal with it.

For Korean audiences, much of Poetry's resonance no doubt comes from the casting of Yun Jung-hee, a respected Korean actress returning to the screen after 16 years. Non-initiates like me won't see any obvious grande dame status in Yun's quietly devastating performance, but rather a composure, a contained intensity and a residual streak of flirtatiousness in Mija's manner. In some of the character's solitary moments, we realise that this quiet woman, with her floral tops and flouncy scarves, still clings regretfully, painfully to the memory of the seductress that she once was.

This flawlessly constructed, bitingly intelligent film really does find poetry in the everyday – but a poetry as savage as it is contemplative.

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