There’s a scene in “The Help,” the new movie based on Kathryn Stockett’s novel, that cracks open the early-’60s world of strained smiles and gentility that rarely leaps out of this big, ole slab of honey-glazed hokum. It’s after hours, and Aibileen, a maid played with determined grace by Viola Davis, is going home. Suddenly the bus stops, and a white man orders the black passengers off, explaining that a black man has been shot — except that he doesn’t say black, Negro or colored. In a pool of dreadful night, Aibileen and a young man trade goodbyes and rush off. And then this sturdy, frightened woman starts running as if her life were in danger, because it’s Mississippi, and it is.

When she gets to safety, Aibileen learns that the man who has been shot is Medgar Evers, the civil rights activist who was gunned down in Jackson, Miss., on June 12, 1963, in front of his home. His wife and three young children, who were trained to lie on the floor in case of gunfire, found him, and Evers died shortly afterward. Hours before, President John F. Kennedy, spurred on by different national events, including the demonstrations in Birmingham led by the Rev. Dr. Martin Luther King Jr., had delivered his landmark speech about civil rights. He said we were facing a “moral crisis as a country and a people” and soon introduced legislation that would become the Civil Rights Act of 1964, the same year “The Help” rises to its teary, insistently uplifting end.

If the movie’s director, Tate Taylor, had his way, your tear ducts would be sucked dry by that big finish, emptied out by a pileup of calamities that include a painful romantic breakup, the devastations of cancer and the mighty wailing of an emotionally abandoned toddler. And that’s just what’s ailing the white folks. The black characters have it tough too, no question, and Mr. Taylor includes enough scenes of Aibileen and her best friend, Minny (Octavia Spencer), cleaning white houses and polishing the silver — and cooking meals and tending children and smiling, always smiling, even as they pretend not to hear the insults — to remind you that this is at least partly about backbreaking, soul-killing black labor.

Aibileen works hard for one family in Jackson, minding a pale dumpling named Mae Mobley, whose own mother, Elizabeth (Ahna O’Reilly), called Miss Leefolt by Aibileen, scarcely touches the child. Aibileen loves the white babies she helps raise, though that affection comes with so many choking complexities that they can leave her near-speechless, as the promising first scene shows. Did you always think you would be a maid? an off-screen woman asks. Aibileen answers quietly but with matter-of-fact directness, yes: Her mother was a maid, and her grandmother had been a house slave. Did you have dreams of being something else? the unseen woman asks, her voice so guileless and so maddeningly oblivious that it’s a wonder that Ms. Davis, who has been looking directly into the camera, nearly burning right through it, doesn’t sneer.

But Ms. Davis keeps her cool even as she warms your heart and does her job, often beautifully. She doesn’t just turn Aibileen, something of a blur in the novel, into a fully dimensional character, she also helps lift up several weaker performances and invests this cautious, at times bizarrely buoyant, movie with the gravity it frequently seems to want to shrug off. She keeps your attention focused on her and Minny even when the story drifts over to Elizabeth and her white friends, who include a segregationist housewife, Hilly (Bryce Dallas Howard, energetic in a thankless role), and the far more liberal Skeeter (Emma Stone, uncharacteristically wan). A would-be writer, Skeeter is the one asking Aibileen all those questions.

The story, which Mr. Taylor adapted for the screen, involves Skeeter’s attempts to interview Aibileen, Minny and others about their experiences as maids. Skeeter, recently graduated from the University of Mississippi, has returned home to find that Constantine (a frail-looking Cicely Tyson), her family’s longtime maid and the woman who raised her, has disappeared. As Skeeter tries to find out what happened to Constantine — Skeeter’s ill mother, Charlotte (Allison Janney), isn’t saying — she begins a process of discovery. She lands a newspaper job, meets a boy (Chris Lowell) and slowly starts to see her friends for the bigots they are. Alas, she doesn’t cozy up to the only interesting white woman in town, Celia (a winning Jessica Chastain), a bottle blonde shunned by almost everyone but her own maid, Minny.

Mr. Taylor handles these story threads ably as he moves from one household to another, from the bright, open plantation where Skeeter lives to the shotgun shacks that Aibileen and Minny call home. Everything looks good, polished to a high industrial gleam. Save for Ms. Davis’s, however, the performances are almost all overly broad, sometimes excruciatingly so, characterized by loud laughs, bugging eyes and pumping limbs. Ms. Chastain and Ms. Spencer make quite the raucous comedy team, and while there’s pleasure in their routine, all that comedy can feel misplaced. They have some genuinely touching moments together when you see two women, each struggling with the burdens of race and class. But just when you think it might get too heavy, Minny starts vacuuming a stuffed bear for some laughs.

Born in Mississippi in 1969, Ms. Stockett, a white woman, has suggested that she was somewhat inspired by Demetrie McLorn, a black woman who worked as a maid for her family, who died when Ms. Stockett was 16 and spoke, to judge from the book’s afterword, in dialect. Some readers have objected to Ms. Stockett’s decision to use black dialect that, in the case of Aibileen, is so thick and old-timey (“sho nuff”) that it’s as if Ms. Stockett were trying to channel Mark Twain. Her white characters, by contrast, are mostly written in “correct” English, even Celia, who in less genteel quarters would be called poor white trash. The dialect doesn’t register as weighty in the movie, largely because Ms. Davis’s performance speaks louder than her accent.