Aside from implying that the true meaning of Christmas involves something close to incest, “The Family Stone” is an amusing, entertaining holiday film. Though its heart isn’t in quite the right place, by the time that is revealed, there have been enough amusing, warm, and funny moments to stumble through to the credits.

The Stone family is the quintessential Northeastern liberal clan – all the way down to the sign language they’ve mastered to accommodate the deaf, gay son. A group of intellectuals and artists, they are quirky, socially aware, and open-minded – as long as everyone agrees with them.

But when their oldest son, Everett (Dermot Mulroney), brings home his girlfriend, Meredith (Sarah Jessica Parker), they are unwilling to welcome this misfit into their family. She works in finance; more horrifyingly, she expresses opinions that differ slightly from their own. At one point, she even suggests that being gay might be more difficult than being straight (for this sin, she is run from the room).

The relationship between Mr. Mulroney and Ms. Parker never stands a chance against the Stones. Mr. Mulroney plays at being charming for much of the film. When he finally picks up a personality, however, he comes across as smarmy.

For her part, Ms. Parker – going against type as an uptight New Yorker, rather than the slutty New Yorker we’ve come to know and love – doesn’t come into her own until, as the plot requires, she discards most of her character’s personality traits.

Ms. Parker’s quirks are there mainly to showcase the various reactions of the Stone family. The Stones are bullies – they only accept Meredith after they’ve decided she has become sufficiently like them. Yet their closed-mindedness often makes the Stones an amusing bunch to watch.

Diane Keaton and Craig T. Nelson, as the parents, share an easy, natural warmth. Their children are all played by a generally capable cast, but Rachel McAdams and Luke Wilson keep the film afloat. Ms. McAdams reasserts her ability to find the heart even in the shallowest of characters, while Mr. Wilson again breathes life into the quirky lover-boy role.

Writer-director Tom Bezucha has fully captured the feeling of the New England holiday season. And from the cluttered coziness of the Stone household to Ms. McAdams’s bed-head, Mr. Bezucha oversees an ensemble that seems impressively true to life.

Indeed, the first three-quarters of the film are so effortlessly entertaining, and so good at avoiding the cliches that plague most holiday films, that you’ll overlook the conventional story and gaping holes in plot. But in the last 20 minutes, it all comes tumbling down.

Mr. Bezucha tracks down every single loose end in the plot and ties them all together in a big, unfortunate knot. While some of his fixes work, others ring false, and still others are just plain creepy. The final wrap-up feels more confused than poignant, but once again Mr. Bezucha is helped by the caliber of his cast – Ms. McAdams smooths things over until the credits roll.

Many families find themselves looking for a Christmas movie to see during the holidays. Considering how many other recent Christmas films involve Tim Allen or Billy Bob Thorton doing embarrassing things in a Santa suit, you could do worse than “The Family Stone.” Mr. Bezucha has chosen a genre with very low standards but exceeds them admirably.