Broken English begins with the face of its heroine, Nora Wilder, positioned between two glasses of wine. This is a place where Nora finds herself most of the time. But as imagined by director Zoe Cassavetes (yes, the daughter of John) and inhabited by Parker Posey, Nora isn't a typical movie drunk, smashing from one blinding binge to another. She self-medicates the way real people do: She feels intoxicated because it's better than feeling something worse. And there are many worse things Nora could feel: lonely, floundering, panicked at going nowhere with no one. "I think I must be doing something horribly wrong," she admits through tears. "But I don't know what it is."

Parker Posey could be forgiven for thinking the same thing. For the better part of a decade, she's been the indie "it girl," the one who stole small movies out from under the clever boys directing them. In the late 1990s she breezed through successes: a sardonic girlfriend in Noah Baumbach's Kicking and Screaming, a Jackie O-obsessed seductress in House of Yes, and the strange, magnetic Fay Grim, the suburban muse for Henry Fool. (She may still be best known, however, as the bullying senior who made those freshman bitches fry like bacon in Dazed and Confused.) In these roles, she combined her striking features—hard mouth always prepared with a scowl, dark, wary eyes, and hands perpetually capturing a passing cigarette—into a single, defined character: the beautiful woman with the bullshit detector. But that act has yielded diminishing returns; to be precise, it's yielded Superman Returns, and a role as Lex Luthor's mistress. Even another pass at Hal Hartley and Fay Grim earlier this year was more an exercise in camp than anything else.

So it makes for a sort of poetic justice that Posey's best performance in years is as a woman who needs saving. At first glance, Nora seems a bit of a joke, a depressing variation on the cardboard neurotics who populate New York romantic comedies. She endures a series of humiliating dates: first with a shitheel actor (Justin Theroux) and then with a spineless family friend (Josh Hamilton—and come to think of it, where has he been since Kicking and Screaming?). She's sipping her way through another party when in bounds Julien (Melvil Poupaud)—lanky, French and possessed with the remarkable ability to make a straw hat look sexy.

It's not terribly difficult to imagine where Broken English goes from there—insouciant foreigners are a reliable cinematic tonic for nervous Americans—but it's not so easy to predict where Posey goes with her character. She doesn't blossom, coo or unwind. She cracks. And the fissures expose dimensions of acting that Posey has never shown before. She has a little speech in an aquarium—no more than 30 seconds long, and about penguins, of all things—that ranks among the finest, most affecting displays of vulnerability I've ever watched on a screen. That Posey finds these emotions, and that Cassavetes captures them, means that two artists are doing something wonderfully right. And it's something that needs to be seen.