Eighteen-year-old Tracy (Lola Kirke) desperately wants to be a writer. At the beginning of her first semester at Barnard in New York City, she meets Tony (Matthew Shear), another student with literary aspirations. They become friends and Tracy has high hopes for the relationship. She falters in her resolve after being rejected for membership in a snooty literary society and then is shocked by the discovery that Tony has a jealous girlfriend named Nicolette (Jasmine Cephas Jones) who doesn't take too kindly to their friendship.

In a conversation with her mother (Kathryn Erbe), Tracy describes her feelings of loneliness by saying, "It's like being at a party where you don't know anybody all the time." Her mother who is about to marry again, suggests that Tracy get together with Brooke (Greta Gerwig), her soon-to-be stepsister. This 30ish young woman has a flair for the dramatic. Meeting Tracy at Times Square, she strides down the platform of stairs behind the discount TKTS booth like a bonafide celebrity.

Brooke is one of those persons who talks fast, possesses phenomenal energy, and is regularly filled with new dreams and entrepreneurial schemes. Tracy spends one evening with her and is astonished at the breadth of her interests in interior design, aerobics (she leads a cycling class), and her biggest project of all: starting a family-style restaurant which will be a combination bistro, hair salon, and art gallery. Her Greek boyfriend, who is currently overseas, is the main investor.

The longer Tracy stays with her stepsister, the more she is troubled by her mood swings and her embarrassing response to a fellow high school student who was hurt by Brooke's ridicule of her in high school; this woman vents her anger and walks away. Brooke has a knack for drawing out the worst in others as evidenced by her rift with her former best friend Mamie-Claire (Heather Lind) who stole her idea of marketing a t-shirt and made a lot of money for herself. When Stavros pulls out of the restaurant project, a medium advises Brooke to get in touch with Mamie-Claire who now lives in Greenwich, Connecticut, with Brooke's wealthy ex-boyfriend Dylan (Michael Chernus).

Spurred on by all the adventures she is having with her stepsister, Tracy creates a short story about Brooke and finds herself in suburban Connecticut defending her right to create a work of fiction by altering the details of a person's life. With great elan and wit, director Noah Baumbach (The Squid and the Whale and Margot at the Wedding) and co-screenplay writer Greta Gerwig deliver a sequence of very funny scenes at Dylan's luxurious house revolving around wealth, friendship, betrayal, resentment, creativity, and boundaries.

Gerwig is center-stage in this frolicsome comedy but it is Lola Kirke who steals the show with her sensitive narration and nuanced performance of a young woman who learns to follow her own spirit, no matter what the circumstances. Brooke is frequently irritating, but in the end our heart goes out to her as she laments "Being a beacon of hope for other people is a lonely business." She certainly fulfills that service for Tracy.