White is the color we associate with weddings, but "Rachel Getting Married" deals in shades of gray. From a distance, it looks like a tasteful dramatic comedy of matrimony among the ownership class.

Then the bride's prodigal younger sister erupts on the scene, fresh out of a nine-month stint in rehab and radiating narcissism, resentment and sexual tension. Soon, the round of bridesmaids' fittings, seating arrangements and champagne toasts are threatened by an unchained personality with no patience for convention and ritual. The instant you clap eyes on Anne Hathaway as Kym, a spiteful, spontaneous, charismatic nuisance, you know that she might rupture the wedding, but she'll do it with flair.

Jonathan Demme directs Jenny Lumet's screenplay as if it were a free-flowing, improvisatory project from his documentary days. He pushes viewers into the thick of familial conflicts and prods us with just enough information to figure them out for ourselves. Demme's spying on the characters with us as accomplices. It's the tension between the unpredictable activity in the background and the scripted social activities at the front of the scene that gives the movie its suspense.

What we see is a gallery of surprises loosely pinned to the rituals of the groom's dinner. (Kym discovers that the best man is a fellow 12-stepper, and Demme teases us to guess how they'll undermine each other's rehabilitation. They do, but not in the way we'd predict, and not with the consequences we'd expect.)

The film is less interested in telling a story of contrivances, coincidences and neat resolutions than in exploring real human responses. It's all about tone, not story line. That approach, an almost improvised search for the meaning of the tale, places a lot of responsibility on the actors' shoulders, and some are more capable than others. Bill Irwin is periodically brilliant as the fussbudget WASP patriarch. Debra Winger, playing his world-weary ex-wife, effortlessly takes command of every scene she plays; what a shame that she's been out of sight for so many years. Winger looks on with a silent sigh as her girls squabble; she's too dignified to dramatize her disappointment and too wise to hang around moping, so she makes a brief appearance, says the right things and gets back to her own life.

It's Hathaway's extraordinary performance that is the film's brightest accomplishment, however. Her Kym is a portrait of disjointed emotions, scarcely repressed anger and ferocious intelligence without a constructive outlet. When we learn that Kym had a flourishing, unhappy career as a fashion magazine model, it makes perfect sense. She's self-indulgent enough to want success without much effort, iconoclastic enough to resent a business that places such an absurd premium on appearance. She is as intriguing, flawed, irritating and delightful as the film Demme constructed around her.