Noah Baumbach’s "Mistress America" advertises itself as a screwball comedy. But this smart, fast-paced film is not really the zany, lighter-than-air divertissement that the term usually conjures. There are scattered sharp one-liners, but not enough to infuse the movie with a sustained bonhomie. It’s fair to say that "Mistress America" revises and subverts this most buoyant of genres with a steady undertow of anxiety, dread and anger.

As in all of Baumbach’s films, the characters are nervous, insecure and acutely self-conscious. Even in the climactic comic set piece of sustained, high-velocity banter, the rat-a-tat-tat dialogue is tense and seamed with hostility, suspicion and hidden agendas.

"MISTRESS AMERICA" Rated: R Opens Friday at Kahala 8

The characters include one authentic madcap in the classic screwball tradition of Carole Lombard and Jean Arthur. Brooke (Greta Gerwig), a peripatetic New York gal about town, is the movie’s captivating energy source. Spectacularly embodied by Gerwig, who wrote the screenplay with Baumbach, she is a movie archetype out of time, and Gerwig’s charm is such that she makes Brooke lovable even when she’s a flake.

Brooke appears to lead a charmed life at the center of a traveling three-ring circus. She has a million grand schemes, of which the most urgent is her plan to open a restaurant in Williamsburg, Brooklyn, with the backing of a Greek boyfriend, Stavros. This future eatery, Mom’s, is a combination bistro, hair salon, art gallery and homey retreat for the hipoisie. And while juggling to keep many balls in the air, she still has the time to lead a spin class.

What distinguishes 30-year-old Brooke from most New York women on a fast track is her willful naivete. She talks a mile a minute, but is neither a shameless name-dropper nor a compulsive networker. Even when disparaging someone else, she doesn’t sound bitchy so much as mystified.

The story is sporadically narrated by the 18-year-old Tracy (Lola Kirke), Brooke’s soon-to-be-stepsister, whose mother, Stevie (Kathryn Erbe), is about to marry Brooke’s father. Tracy, who wants to be a writer, has just begun her first semester in college. Bored with her classes, she has few friends and is rejected for membership in a prestigious literary society. Brooke, whom she first meets in Times Square, pulls Tracy out of her slump, and the pair become gal pals.

Brooke’s bubble begins to burst when Stavros abruptly pulls out of the restaurant deal, and Brooke has to scrounge for other investors. In desperation, she gathers a posse that includes Tracy, Tracy’s classmate Tony (Matthew Shear), and Tony’s possessive girlfriend, Nicolette (Jasmine Cephas Jones). Together they drive to Greenwich, Conn., to entreat Brooke’s rich ex-boyfriend Dylan (Michael Chernus) to save the day.

A nice guy who doesn’t lord his wealth over others, Dylan hasn’t seen Brooke since her former best friend Mamie-Claire (Heather Lind) stole him from her, along with her idea for a T-shirt from which she earned a handsome profit. When the posse appears at the door of Dylan’s mansion, a scowling Mamie-Claire answers the door.

Beginning with Baumbach’s 2007 film, "Margot at the Wedding," the concept of artistic appropriation and the piracy of inspiration has loomed large in the director’s canon. But in the backbiting world of "Mistress America," it is understood that you do what you have to do to get ahead, even if it means sacrificing a friendship.

Mamie-Claire and Nicolette are two of the meanest female characters to be found in a contemporary film, especially one with an upscale, literary setting. Shallow, treacherous, jealous and vindictive, they cast a pall of ill will over a film that can’t transcend the petty demons nipping at its characters’ heels. Levity is just not Baumbach’s thing.