Great stories don't have to be grand epics. Some unforgettable stories come from characters traveling the distance of baby steps. Case in point: "Precious," an engrossing portrait of a marginalized Harlem schoolgirl. Precious Jones (Gabourey Sidibe) begins her journey trapped in an abyss of inner-city poverty and abuse. We leave her on a hushed note of expectancy. The film is not a wallow in pathos but a rare and remarkable call to empathy.

At 16, Precious is self-isolated, depressed to the point of shutdown. She is near-illiterate, obese and impregnated for the second time by her father. She's taunted and shoved by her equally maladjusted peers. In fantasy sequences Precious flees to a vacuous dreamland of stardom, glamour and handsome boys. She has so much self-loathing that when she primps at her bedroom mirror, her reflection is a lithe blonde.

Initially we can't read much on Sidibe's impassive face; director Lee Daniels hints she's deeper than we assume. Notice the color-coordinated plastic necklaces she wears with her shabby school clothes. The girl has an eye for beauty.

Daniels (who produced "Monster's Ball") carries us into Precious' tawdry world with pungent realism. He's a masterful filmmaker, fully in command of troubling, taboo-tackling material.

He addresses issues such as petty crime, welfare fraud and emotional, physical and sexual abuse with candor. Working from a low-budget documentary aesthetic, he gives every shot the tang of unflinching objectivity. Closeups show the actors' blemished skin. When Precious prepares meals for her harridan mother, Mary (Mo'Nique), you smell the rancid grease in the frying pan.

This resolute adherence to authenticity extends to the characters' painful emotional lives. Mary reigns over their squalid apartment like the queen of hell. She keeps Precious on hand only to protect her welfare stipend and run her errands, subjecting the girl to barbaric cruelty. Part of the film's power is that it sees the vestiges of humanity in this monster. Mary knows her best years have gone. She feels a twisted sexual jealousy toward her daughter. Those are merely explanations for Mary's cruelty; they don't excuse her.

In the same spirit, Daniels refuses to douse Precious with tragic nobility. She's a petty thief, a seriously underskilled mother and, for much of the film, a passive victim. Despite the film's clear social conscience and sympathy for the community it portrays, "Precious" never panders for compassion. This is not a film about sociology. It's a platform for uncommonly truthful acting, and that's what Daniels gets from his performers.

Mo'Nique is menacing in emotionally jagged scenes where Mary attacks Precious for "stealing" her man. This is not the kind of turn where you understand the character because it's artfully written and vibrantly enacted. You believe Mo'Nique, because you accept that her character's behavior is coming from some haywire rat's nest of damaged brain circuitry.

In her more restrained role, Sidibe is an out-of-nowhere phenomenon. She can anchor a scene just by walking in. Mariah Carey goes convincingly washed-out and drab-haired as a sympathetic welfare official.

"Precious" has a raw, uncompromising tone, but it's not an unrelenting agony bath. Solid laughs are hidden where you don't expect them. Precious complains about crack dealers "givin' the ghetto a bad name." Her schoolmates' antic misbehavior is amusing without being movie-cute.

When Precious transfers to a remedial school, a team of battle-weary but committed teachers and caseworkers help her begin to change her life. There are crushing setbacks along the way; one good year can't erase a lifetime of fractured relationships. Her teacher, Ms. Rain (empathetic Paula Patton), encourages Precious to exorcise her demons by writing her story. It's a tentative stride down the path to adult responsibility, hinting at the possibility of redemption in a coldhearted world.