The mind works in mysterious ways. Confronted with terms like "quiet" and " subtle", the majority will switch off. By contrast, "Oscar" and "winner" provide huge stimulation. And whether or not you approve of such excitement, it's clearly what the distributors of Sarah Polley's quiet, subtle Canadian film are banking on.

Away From Her was released last April and attracted very few punters. What's the betting - now that its star, Julie Christie, is expected to win a Best Actress Oscar later this month - that things will be different on its re-release?

Away From Her struck me as wonderful when I first saw it and stands up beautifully to a second viewing.

The story, weaving backwards and forwards in time, is both simple and complex. A woman in the early stages of Alzheimer's, Fiona (Christie), goes into a home called Meadowlake, falls in love with a fellow patient, Aubrey (Michael Murphy), and has her heart broken when he leaves. Because her husband, Grant (Gordon Pinsent), loves his wife, he tries to renite them.

The complication is that Grant - a retired professor - had at least one affair with a student during the Sixties sexual revolution. He can't help but wonder if Fiona's infatuation with Aubrey - and inability to recognise their 40 years of marriage - is a form of punishment.

Meanwhile, he attempts to ensure Aubrey's return to the home by entering into a relationship with Marian, Aubrey's lonely wife. He thinks Fiona's feelings for Aubrey are a "charade". How real are his feelings for Marian?

Writer-director Polley adapted the script from a short story by the sublime Canadian writer Alice Munro. And although almost all of the best lines are lifted straight from the page, Polley has put her own stamp on Munro's tale.

In the story, the husband is a cynical philanderer who almost accidentally changes his ways (he thinks - wrongly - that his wife knows nothing about his indiscretions). In the film, by contrast, he is all soft crumples. More importantly, it's immediately clear that Fiona knows about his past.

Polley, basically, has nudged Christie's character into the foreground. Spikily determined, this rewritten Fiona enjoys teasing her husband, quoting one of his old flames before adding, eyes narrowed, "Don't be nervous, it's a good story..." It's she who, on the day her husband brings her to Meadowlake, decides they should have sex, then insists he leaves without looking back.

It's annoyed some critics that Fiona often seems at one-remove from her illness. But the point about this character is that she's at one-remove from herself. She's a well behaved bohemian, always on the hunt for freedom, always afraid of the damage such freedom might cause. Alzheimer's doesn't interfere with such confusion, it expands upon it.

A peculiar product of her time, Fiona fits Christie like a second skin. The 66-year-old actress has a fragility about her, a delicacy, that has often led directors - foolishly - to drape her in period clothes.

Ironically, in so many of these films - Far From the Madding Crowd, The Go-Between, more recently Finding Neverland - what you notice is her sulky sturdiness, her fidgety, modern self.

She's infinitely better when allowed to float in the present day. She was gut-wrenchingly vulnerable in Don't Look Now in 1973. She's just as raw here. No wonder she won this year's Evening Standard Alexander Walker lifetime achievement award.

Thanks to her performance, we find it easy to accept Grant's obsession with Fiona, but even easier to believe in the latter's insecurities. Christie doesn't try to keep her face immobile, like some screen beauties. Lost in the snow, bundled up in tracksuit, she looks like a stricken bag lady.

The surprise is that this film contains two great female performances. Olympia Dukakis plays Marian, the lower-middle-class, supremely proud wife of Aubrey who yanks him out of Meadowlake in order to save the one thing she loves - her home.

Through her, we gain a sense of the economic realities Grant and Fiona never have to consider. And via her wary, defiantly peculiar face, we come to realise the obliteration that so often accompanies plainness. Fiona's illness makes her feel that she is "disappearing". Marian - as far as the wider world is concerned - has always been invisible.

This is a mature work, in every sense of the word, from 29-year-old Polley. Best known as an actress, she turns out to be a natural unseen presence, a prodigious manipulator. It was Polley who thought of Christie for the part (they'd acted together in two films and become friends); it was she who nagged the allbut retired actress until Christie gave in.

With very little money, Polley has created a white world - the white of snow, milk, sheets, sunshine, old-lady hair and blank terror - that dazzles.

True, she gets a few things wrong. There's a sappy "moment" with a grungy teenager. Fiona's firm-but-fair nurse, Kristy, looks - and occasionally sounds - like the Vicar of Dibley. And the penultimate scene is confusing. But these are mis-steps, not disasters.

Away From Her is a love story with no fixed beginning or end, a romance about the power of the past and the futility of second-guessing the future.

Go and see it for Christie's almost-certain-to win-an-Oscar performance. Go and see it because it's quiet and subtle and reminds you that there's more to life than coming out on top.