Precious (15)

Very hard times in Harlem

There are hard luck stories, there are stories of sick relationships, and there is Precious. Or, to give the film its full, ungainly title, Precious: Based on the Novel 'Push' by Sapphire, a literary source said to be even more unflinching in its chronicle of ignorance, misery and sheer barbaric wrongdoing. Forgive me if I don't rush out to buy a copy.

The heroine and narrator of the story is one Claireece Jones (Gabourey Sidibe), a morbidly obese and illiterate 16-year-old growing up in a Harlem tenement in the late 1980s. The girl calls herself Precious, a hideous irony given how little cherished her life has been up to now. Having given birth aged 12 to a child with Down's Syndrome – cheerfully called Mongo – Precious is pregnant again, and has been expelled from school.

It gets worse: the man responsible in both cases is her own father, who, we gather from a squalid flashback, raped her. Her mother, Mary (Mo'Nique), is a welfare-chasing couch potato who serves up a diet of physical and verbal violence, bitterly resentful of her daughter for "taking away" her man. "I shoulda aborted your motherfuckin' ass," she spits.

There is an almost Dickensian horror about this household of abuse, except that Dickens would have sentimentalised the heroine as a bruised angel. Precious is not that. Her addiction to junk food – check her ordering fried chicken in a basket the size of a small skip – has rendered her face so bloated that her cheeks have made slits of her eyes. She has the wide-stepping gait of the grotesquely fat, and neighbourhood toe-rags hurl insults and push her over. What refuge is there for this poor thing? Well, there's the one inside her head, aglow with fantasy images of herself as a disco diva, a red-carpet celebrity and, in one haunting mirror reflection, a thin, white blonde.

A more practical alternative to these illusions comes in the form of a local teaching program that offers help to hardnuts and misfits like herself. "Try for a better future!" is its rallying call, though for Precious any future at all would be welcome at this stage. It's also a ray of light to the audience suffering in the dark, though you may find her teacher Ms Blu Rain (Paula Patton) reminiscent of those conveniently inspirational educators who turn around the lives of difficult urban kids – think Michelle Pfeiffer in Dangerous Minds or Hilary Swank in Freedom Writers. Ms Rain, rather sleek and well-dressed for a state-funded teacher, doesn't become overbearing with piety, but she's still more a figment of the liberal imagination than a convincing human being. If I also told you there's a social worker played by Mariah Carey you'd probably groan and cross Precious off your list right now, but the astonishment of it is that Carey's not half bad in the role – unglamourised, barely made-up, sensible and straightforward with a won't-get-fooled-again sort of humour.

It's also true that the script, by Geoffrey Fletcher, keeps warning us to resist its own feel-good embrace; it won't allow too much sunshine to illuminate the dark mood. Precious, striving for a better life through education, has still enough hard-edged cynicism to know that words alone won't help her. "The longest journey begins with a single step," she reads on a poster... "whatever the fuck that means," she adds. When Precious returns from the hospital with her second child, her mother asks to cradle the infant, and for a few moments we glimpse the possibility of an unprecedented outbreak of maternal warmth. Next minute, reminded of the child's father, Mary makes a savage attack on Precious, who eventually tumbles with her baby halfway down the tenement steps – followed by the TV set that the unfond matriarch has aimed down the stairwell.

So staggering, in fact, are the offences to decency, loyalty and love that you begin to worry that the film will topple over from the weight of its woes. Even now the Wayans Brothers are probably cooking up a moronic parody of Precious, which will involve a load of crass jokes about bulimia and obesity (they'd call it "Issue Movie" if they knew what it meant). Yet the director Lee Daniels (who produced Monster's Ball) has a sense of humour to leaven the sense of outrage, and within the crew of classmates – Stephanie Andujar, Chyna Layne, Amina Robinson, Xosha Roquemore – who trade a sardonic patter on the sidelines the film orchestrates its funniest scenes. The number of strong women roles is quite unusual for a movie of this kind; men barely figure in it, aside from Lenny Kravitz as a friendly hospital worker. Significantly, Precious's rapist father is seen only at midriff level, the implicit question being: why should he be allowed to show his face?

The moral uplift of Precious isn't quite convincing, and however much Oprah Winfrey contributed as an executive producer, her name on the credits is not an unarguable blessing. Yet the film deserves a wide audience, and it ends very powerfully. Mary, the mother, has been such a loathsome presence that you hardly notice what an amazing performance it has exacted from Mo'Nique, an acclaimed stand-up in the US who here bravely repels our smallest urge to sympathise with her. Until the end, that is, when she somehow curbs her foul-mouthed hostility in a desperate apologia pro vita sua. And I do mean "desperate" – this is a monologue delivered with such hoarse-voiced pleading that it barely looks like acting at all. It's pathetic and sordid and indefensible in content, but that won't prevent you being horribly moved. Oscar might think so, too.