American Isabel Walker (KATE HUDSON) has arrived in Paris to see her pregnant half-sister and poet, Roxeanne de Persand (NAOMI WATTS). Just as Isabel arrives, however, Roxeanne's painter husband, Charles-Henri (MELVIL POUPAUD), is leaving. He's fully intent on divorcing his wife for Magda Tellman (RONA HARTNER), a Russian whose American husband (MATTHEW MODINE) is none too happy about this development.
Things become more complicated when Charles-Henri decides he wants half of their joint property that, according to him, includes a Walker family painting. That eventually brings in art experts Julia Manchevering (BEBE NEUWIRTH) and then Piers Janely (STEPHEN FRY) who try to determine whether the painting is by a famous artist and thus worth a great deal of money.
In the meantime, Isabel gets a job working for American author Olivia Pace (GLENN CLOSE) who's preparing to move back to the States. She introduces Isabel to her house painter and fellow social worker, Yves (ROMAIN DURIS), while also setting up Roxeanne with a lawyer, Maître Bertram (JEAN-MARC BARR), who will help her in the pending divorce proceedings.
At the same time, Isabel agrees to become a mistress to Edgar Cosset (THIERRY LHERMITTE), a married French diplomat who once was Olivia's lover and is Charles-Henri's uncle. That doesn't sit well with his sister, Suzanne (LESLIE CARON), who otherwise seems to enjoy watching the Americans squirm, including when the sisters' parents, Chester (SAM WATERSTON) and Margeeve (STOCKARD CHANNING) and brother Roger (THOMAS LENNON), suddenly show up.
With Isabel dealing with her relationships with Edgar and Yves, Tellman becoming increasingly edgy over his wife running off with another man, and Roxeanne trying to deal with her pending divorce, the American sisters learn that intercontinental romance is more complicated than they ever imagined.