Sometimes, if you're lucky, you can watch someone become a movie star in a single scene--Al Pacino in the Solozzo assassination scene in The Godfather, say, or Tom Cruise sliding into his living room in Risky Business. For Greta Gerwig, that moment comes about 2/3 of the way through Noah Baumbach's Greenberg. As Florence, a would-be singer and personal assistant to Phillip Greenberg (Chris Messian), an upscale hotel owner, she has spent most of the story strangely circling her boss's brother Roger (Ben Stiller), an aimless 41-year-old musican-turned-carpenter who is housesitting while the boss and his family are opening a new hotel in Vietnam. But in this key scene, we find Florence alone in her studio apartment, sloppily half-dressed and more than half-drunk, singing along uproariously to Paul McCartney's "Uncle Albert/Admiral Halsey"; she takes a phone call from Roger, humors him a bit, and then makes a stunning confession. In about three minutes, she does a full range of human emotions, and barely breaks a sweat. If her performance here is any indication, this girl's gonna be a damned movie star.

Greenberg is a very smart movie, and a very tricky one--it is not, as we might suspect from its ads, merely another tale of an introvert who has lost his way, and is brought to his senses by the love of a good woman (cue the Garden State comparisons). It is more complicated than that--Roger Greenberg is not a loveable loner, nor an amusing malcontent. He's got real problems, and they manifest themselves in ways that are not easy to get past. Florence is warned that Roger was recently released from a mental hospital, and we slowly piece together his back story; a good decade and a half ago, he was in a pop band, and he was the lone holdout when they were offered a record deal. In the years that followed, he moved to New York and went adrift. "Right now," he tells an old girlfriend, "I'm really trying to do nothing." She replies, "That's a brave choice at our age."

That girlfriend is played by Jennifer Jason Leigh, wife of writer/director Baumbach; she's also credited with co-producing and co-writing the story. She only appears in two scenes, but they're good ones, sticky and truthful. Particularly memorable is a painful coffee meeting between her and our protagonist--he's clearly angling to get back in her life, but as they talk, she's long forgotten even broad outlines of their time together, to say nothing of the specific details he keeps mentioning. It's a relatable but wince-inducing scene, made even more painful by her blunt, immediate response when he takes the next step and asks her out on a date.

Her cold reception is a bit of a relief, as the film seems in danger of setting up a dull, familiar love triangle subplot; Baumbach has nothing so standard on his mind. He's more interested in exploring the hit-and-run dynamic of Gerwig and Stiller's characters; as the story begins, she seems a bit of a flake, and we're not sure how strong her judgment is when she fools around with him during what must be one of the more awkward first dates ever committed to celluloid. Baumbach's intelligent screenplay doesn't make it easy for them--or for us, inasmuch as his peculiar flashes of temper and seeming insistence on being troublesomely mean to her doesn't exactly set up the kind of rooting interest we've come to expect from our cinematic would-be romances. But the nuanced screenplay puts the onus for the relationship on her, and when she mumbles, at a particularly vulnerable moment, "You like me so much more than you think you do," we know she's right.

It takes a very good actress to pull off a role like this, and luckily, Greta Gerwig is a very good actress. She's familiar from several so-called "mumblecore" pictures like Baghead and Hannah Takes the Stairs; cult audiences will recognize her as the obligatory wise-cracking best friend in The House of the Devil. She's a got a great, open face, and a wonderful, natural quality; she can carry off the jokes without playing them for a laugh (like when she drolly informs him, "You can stay over, wink wink"), and can make potentially troublesome lines like "Do you think you could love me?" heartbreaking without sounding pathetic and whiny. Stiller, looking somewhat gaunt and aged, is admirably restrained (this performance recalls some of his more disciplined, honsest-to-God-actor work in films like Zero Effect and Your Friends and Neighbors), while still gracefully hitting the comic beats (particularly when paired with Ryhs Ifans as his former bandmate). He also knows when to turn on the slow boil; a long, strange party sequence towards the end of the film puts him through the acting wringer, and he pulls it off.

The script contains some of Baumbach's most quotable dialogue since his debut film, the incomparable Kicking and Screaming (no, no, not the shitty Will Ferrell movie). When asked how he's doing, Roger responds, "I'm fair-to-middling. Leonard Maltin would give me two and a half stars." When Ifans accuses him of "pulling a Gatsby" by staying inside at his own impromptu pool party, Roger muses, "I don't know that I need to document the reasons this isn't a Gatsby." And when holding court with a group of twentysomethings at a party, he insists, "I'm freaked out by you kids. I hope I die before I end up meeting up with one of you in a job interview." But Roger doesn't get all the good lines, either; Baumbauch is the rare male writer whose women are perhaps more interesting than his men.

His screenplay also takes some risks--he's trying all sorts of interesting ideas and unusual approaches. Not all of them work, but the ones that do pay off in spades. Take, for instance, the long scene towards the end, where Roger opens up while leaving Florence a voicemail message; it should be completely dramatically inert, but the writing and playing is totally dynamic. He also takes on a fascinating look and feel for the picture, which seems, from its soft-rock soundtrack ("you have to look past the kitsch," Roger explains) to the retro title font to Harris Savides' subtly sun-kissed cinematography, to be a throwback to the cinema of the 1970s. Specifically, it plays as a quiet homage to Altman; there's a masterfully constructed scene of uncomfortable party conversations that feels like something out of Nashville, a couple of his signature zooms, and a quirky-character appeal that calls to mind efforts like A Perfect Couple and Thieves Like Us. Don't get me wrong, it's not some empty tribute; Baumbauch melds those influences with his low-key style, and comes up with a nice hybrid of what he's done and what he likes. Greenberg has its problems, yes--the pace is a little punchy, and Roger's neurosis can try the viewer's patience. But it is a smart and sensitive picture, engaging and compelling. And not to belabor the point, but seriously: keep an eye on Greta Gerwig. She's the best thing in this lovely film.

Jason lives in New York. He holds an MA in Cultural Reporting and Criticism from NYU.