In ''The Family Stone," Everett Stone (Dermot Mulroney) brings someone new home for the holidays. She's not a he. (The Stones already have a gay son, who, by the way, they adore.) And she's not black. (Been there, doing that: The gay son's partner.) She's Sarah Jessica Parker, playing an uptight white businesswoman named Meredith.
The Stones happen to be one of those upper-middle-class New England clans whose temperament runs toward the bohemian. So, naturally, Diane Keaton is the matriarch, Sybil Stone. Those of you expecting Peter Fonda as dad will have to settle for a perfectly nice Craig T. Nelson as her large puppy of a husband.
The movie is a holiday romantic comedy that wants to put the holiday romantic comedy out of business. Somebody is gravely (and secretly) sick. Food crashes to the floor. And the wrong people are in love. Yet the sweetness is doled out with a pint of vinegar, so the whole experience is not unlike one of those Hallmark Shoebox Greetings cards: Sarcasm leaking from the heart.
The problem is that no one in this liberal nest of turtleneck-wearing idealists thinks Meredith is right for Everett. She can't hug. Her demeanor runs conservative. She yells when she speaks to Thad (Tyrone Giordano), the gay, hearing-impaired son. And she doesn't handle the withering contempt of Amy Stone (Rachel McAdams) nor the flirting from Ben (Luke Wilson), the slacker-stoner Stone. Desperate for moral support, she calls in her more agreeable little sister, Julie (Claire Danes), to be at her side for the holiday. To Meredith's consternation, Julie fits in immediately.
The first half of ''The Family Stone" is several movies happening at once, and they're all simultaneously overwritten and not fleshed out enough. Writer-director Thomas Bezucha is often less a filmmaker and more a shepherd of pratfalls. You're no one in this movie unless you topple over. (This is his second film; his first was a wonderfully corny little romantic comedy called ''Big Eden," which came out in 2000.)
Nonetheless, most of the cast knows how to navigate the chaos. McAdams is an actress I like more with every movie. She's smart and sly. And Keaton knows how to finesse the movie's drama and comedy -- even though she spends the movie wildly overdressed and her hair has a terrible white streak in the front.
But a few of the actors never come around. As the movie goes on, Parker turns luminously alive, drunk and high with the engaging Wilson. Yet Mulroney mumbles to Danes until her otherwise natural performance is locked up in the halting mannerisms of ''Shopgirl."
It's to Mulroney's disadvantage that we find out almost too late why Everett so desperately wants his mother to give him a family heirloom to slip on Meredith's finger. His thinking suggests a psychologically richer movie.
Instead, ''The Family Stone" continues to beat up on poor Meredith, whose crime is that she's too much like Martha Stewart for this household. She's also required to be a little bit bigoted to Thad and his boyfriend, Patrick (Bryan J. White). The price they pay for not being mincing queens is that they have to be billboards for tolerance: We love our deaf, gay son and his black boyfriend, who are about to have a baby! Why can't you?
The urge to be progressive and politically correct short-circuits ''The Family Stone." This is ''Guess Who's Coming to Dinner" for Air America listeners.
Wesley Morris can be reached at firstname.lastname@example.org.