Under their thick upper crusts, British period pieces can get awfully stuffy or show the strains of trying desperately hard not to be. Yet Stephan Elliott manages to blast some fresh air into the genre in Easy Virtue, an adaptation of a Noel Coward comedy, and he makes it seem almost effortless.

Jessica Biel is Larita Whittaker, an American car racer and pure product of the Roaring '20s who's just married into an old British family with a sprawling country estate.

When she arrives there with her boyish husband John (Ben Barnes), Larita finds a formidable opponent in Mrs. Whittaker (a dowdy Kristin Scott Thomas), a mother-in-law hell-bent on getting her son away from that Yankee tramp.

On Larita's side is the supremely unhappy Mr. Whittaker (Colin Firth), who turns out to be a stronger ally than her own husband.

The witty barbs don't fly as freely as they might in an Oscar Wilde adaptation, but they consistently hit the mark. And every moment is made better by a fabulous ensemble, from a triple-threatening Biel, who also sings and does a mean tango, to a perfectly cast Firth, to Kris Marshall as the extremely handy butler.

Elliott tops things off with a soundtrack mixing songs by Coward and Cole Porter with jazz-aged renditions of "Sex Bomb" and the theme from Car Wash. This one area may be a bit overdone, but it gets by on charm.