Produced by Tyler Perry, the purveyor of cheap soapy entertainment to black America, and Oprah Winfrey, who needs no introduction. Guest starring Lennie Kravitz and Mariah Carey. These are ominous words. Yet if Precious makes painful watching (and it does), it isn't for the reasons common to vanity projects. Adapted by Lee Daniels from a novel by the performance poet Sapphire, the film tells the story of Claireece Precious Jones (the impressive newcomer Gabourey Sidibe), an obese teenager who is expelled from school, enslaved and terrorised by her welfare jockey mother and impregnated for the second time by her own father. Despite these setbacks she finds her way on to a remedial literacy course along with a multicultural crew of young women and together they blossom under the care of a dedicated teacher. The horror of Precious's circumstances notwithstanding, this ought to be a recipe for mere mawkishness, a thank-you card to America's front-line social services. That it isn't is a tribute to the look of the film, at once gritty and hypnotic, full of hazy overexposures and lush fantasy sequences, and to the calibre of the performances. Mariah Carey dutifully effaces her star persona as a dogged social worker and Sidibe's heroine delivers the required cocktail of pain and fortitude without visible self-consciousness. No cast member is so striking as Mo'Nique, however, who paints Precious's mother with such a mesmerising combination of self-pity and savagery, the cinema didn't see a more believable monster all year. She earned her Oscar.