Gatsby Welles, Timothée Chalamet, is the brainy but eccentric son of wealthy New York City–based parents and a student at Yardley College, a liberal arts school in upstate New York. He is also a skilled gambler. When his girlfriend, Ashleigh Enright, Elle Fanning, a journalism major from Tucson, must travel to Manhattan to interview the esteemed independent film director Roland Pollard Liev Schreiber for the student newspaper, Gatsby tags along, planning a romantic weekend in the city, while trying to avoid his parents who are hosting a gala in the evening, and with whom he has a conflicted relationship.
Ashleigh's interview with Pollard is supposed to last one hour, but the director invites her to a private screening of his new film, which ruins her plans with Gatsby, much to his dismay. Strolling alone through New York, Gatsby bumps into a film student friend who asks him to stand in for a missing actor for a shot that involves kissing his co-star. To Gatsby's surprise, the actress turns out to be Chan Tyrell, Selena Gomez, the younger sister of a former girlfriend. The two run into each other again when they hail the same cab. Gatsby's romantic plans are further delayed by Ashleigh growing closer to Pollard, who is having a creative crisis, and his long-suffering screenwriter, Ted Davidoff Jude Law.
Feeling abandoned and adrift, Gatsby accompanies Chan to her parents' apartment where he sings "Everything Happens to Me" on their piano. They discuss their love for New York and agree that, on rainy days, it is one of the most romantic places. They visit the Metropolitan Museum of Art, where Chan confesses that she once had a crush on Gatsby. A chance encounter with his aunt and uncle at the museum forces Gatsby to attend his parents' gala later that evening.
Meanwhile, while searching for a vanished Pollard, Ashleigh and Ted stumble upon Ted's wife, who is having an extramarital affair. While Ted confronts his wife, Ashleigh goes to the studio where she meets film star Francisco Vega Diego Luna, who invites her out for dinner. Gatsby, meanwhile, uses his gambling skills to win big at a poker game his brother had arranged earlier in the evening. Back at his hotel room, he sees Ashleigh on the television news hailed as Francisco's latest fling. Distraught, he goes for a drink at the Carlyle Hotel's cocktail lounge, where he meets an escort named Terry, whom he hires to impersonate Ashleigh at his family's gala.
Francisco takes Ashleigh to a film business party, where she reconnects with Pollard and Ted, who both declare themselves smitten with her. Afterwards, Francisco and Ashleigh retire to his apartment, and as they are about to have sex, Francisco's girlfriend arrives unexpectedly, driving Ashleigh to leave through the backdoor into the rain, wearing only a raincoat over her bra and panties.
Gatsby arrives at his family's gala with Terry, but his mother sees through the charade. In an intimate talk, she reveals to Gatsby that she was an escort when she met his father, and that her earnings were the seed capital that resulted in their wealth. Her personal history is the reason she has pressured Gatsby into intellectual and artistic endeavors, education, and refinement that she acquired as an adult. This revelation changes Gatsby's perceptions of his mother in a positive way. At the end of the night, Ashleigh finds a despondent Gatsby back at the Carlyle, assuring him that nothing happened with Francisco, despite her lack of clothing.
The next morning, before their planned return to Yardley, the pair take a horse-drawn carriage ride in Central Park. Ashleigh, however, is disappointed by the misty weather, and when Gatsby mentions a Cole Porter lyric, she misattributes it to Shakespeare. Realizing their incompatibility, Gatsby abruptly ends their relationship and announces that he will withdraw from Yardley to stay in New York. He later goes to the Delacorte Clock, outside the Central Park Zoo, reenacting a fantasy he and Chan previously shared. As the clock strikes six, Chan arrives, and the pair kiss in the pouring rain.
