★ ★ ★ ★ ½

The woman at the center of the feature-length character sketch Mistress America is so beguiling that it’s hard to resist the urge to turn any movie review into a tribute to her: Young Manhattanite Brooke (Greta Gerwig) — cycling instructor, freelance interior designer, and aspiring restauranteur — is an effortless extrovert whose incandescent smile opens doors everywhere, and who has the unique (and unteachable) talent of making the people around her feel special even when she’s talking about herself. She weaves a single bolt of conversation from crisscrossing threads about watching her mother die and finding the best frozen-yogurt place in the city, and pops out Zen bon mots like, “He’s the kind of person I hate, except I’m in love with him.”

“She lived exactly as a young woman should live who wants to spend her youth well,” rightly observes Tracy (Lola Kirke), the mousy Barnard College student who can’t believe her good luck that she and Brooke have crossed paths. Tracy’s mother plans to marry Brooke’s father, which makes the two grown women stepsisters-to-be; this connection gives the lonely Tracy an excuse to reach out to her, a desperate bid to find a companion who isn’t one of her frosty, tweedy classmates. Before long, she’s quietly smitten with the fairy godsister who’s dropped into her life, offering her not only a sympathetic ear, but an example of the kind of person she hopes to become one day. (This movie contains so many conversations between women, and on so many topics, that it feels as if it’s trying to do penance for all of the films this season that didn’t pass the Bechdel test.) Tracy also has literary ambitions, and she weaves her impressions of Brooke into a short-fiction piece, almost as if by pinning down this rare butterfly, she’ll grow wings herself.

If this doesn’t sound like a Noah Baumbach movie, that it’s much too enchanted to spring from the jaded imagination of the vinegary misanthrope responsible for The Squid and the Whale and Greenberg, credit is most likely due to Gerwig, Baumbach’s lover/muse/collaborator and the Gena Rowlands to his John Cassavetes (and who, unlike Rowlands, shares a screenwriting credit with her director). But, like a child who only begins to resemble his father following puberty, the story takes a puckery turn during the second act, as Brooke needs funds in a hurry and decides to shake down an old acquaintance (Heather Lind) who stole, in ascending order of egregiousness, her fiancé, her cats, and a cool design for a T-shirt. Brooke and Tracy take an impromptu road trip to overmonied Greenwich, CT, where the movie turns into a mannered homage to the madcap comedies of the 1930s — except the sparkling exchanges slowly turn more and more lacerating, as if the leopard in Bringing Up Baby took a moment to maul everyone before the high jinks could continue.

All of Baumbach’s movies (including last year’s While We’re Young) are character studies of frantic, self-thwarting creative types trying to either outrun an encroaching middle age or staggering around like the walking wounded after the world has chewed them up. Even though this film attempts to be a neo-screwball comedy, with Gerwig’s Carole Lombard-like presence giving it lift, it’s still Baumbach Lite: same rancid aftertaste, but now with half the calories. But that may not be such a bad thing. A Manhattan’s not a Manhattan without a dash of bitters, and, despite its raw middle stretch, Mistress America still scintillates with an “anything is possible” effervescence that residents complain the real Manhattan lost a long time ago. No matter what trouble she brought into her life, Tracy is still glad to have spent some time with Brooke — and only the most hard-hearted of moviegoers could disagree.