This multilayered drama revolves around Bobby Dorfman (Jesse Eisenberg) is the youngest son of a Jewish family in New York City in the 1930s. His elder sister Evelyn is a married school teacher, while his elder brother Ben is a gangster. Discontented with working for his father, a jeweler, Bobby decides to move to Hollywood, where he takes a job running menial errands for his uncle Phil (Steve Carell), a powerhouse talent agent.
Phil introduces Bobby to his secretary Veronica, nicknamed Vonnie (Kristen Stewart), who is tasked with helping Bobby settle into Hollywood. Bobby is drawn to her unpretentiousness as opposed to most young women living in Hollywood, and falls deeply in love with her. She rebuffs his advances, telling him she has a journalist boyfriend named Doug. In reality, 'Doug' is Phil, with whom Vonnie is carrying on an illicit romance; he promises to divorce his wife and marry her.
On the first-year 'paper anniversary' of their affair, Vonnie gives Phil a letter written and signed by Rudolph Valentino as a gift. However, Phil proceeds to tell her that he is incapable of divorcing his wife, so he ends the affair. Vonnie subsequently surrenders to Bobby's love for her and their friendship turns into a romance.
A forlorn Phil confides in Bobby about his affair, without naming his mistress, before telling him he has determined to divorce his wife. Bobby passingly mentions his relationship with Vonnie and his intention to marry her and return to New York. Phil begins petitioning Vonnie privately to leave Bobby and marry him instead.
While having a conversation with Phil in his office, Bobby notices the Valentino letter. Recognizing it from Vonnie's account about her breakup with 'Doug', he confronts her and asks her to choose between himself and Phil. Vonnie chooses Phil.
A heartbroken Bobby returns to New York City where he begins to run a high-end nightclub with his gangster brother, Ben (Corey Stoll). It soon becomes a famous hangout for the rich and powerful, from politicians to gangsters. Bobby meets divorcée Veronica Hayes (Blake Lively) at the nightclub, and they begin dating, soon getting married and starting a family together.
On an extended visit to New York, a happily married Phil and Vonnie stop at the nightclub and insist on seeing Bobby. Vonnie has become a pretentious name-dropper and Bobby is at first repulsed by her. However, he agrees to show her around New York—as she had once done for him in Hollywood. They spend an evening without Phil, visiting Bobby's favorite haunts and, as dawn breaks over Central Park, share a kiss; but it's clear that it can go no further.
Bobby's sister Evelyn (Sari Lennick) asks their brother, Ben, to 'talk to' her disagreeable neighbor; Ben promptly kills him. He is arrested and convicted for murder and racketeering. Shortly before he goes to the electric chair, he converts to Christianity, mortifying his parents.
His late brother's notoriety propels the nightclub to new heights, and Bobby travels to Los Angeles to contemplate opening a Hollywood version. He ultimately decides against it, but, before he leaves, he and Vonnie have lunch together, where she mentions that she and Phil will be returning to New York for a short visit. However, they both decide that it is better if they don't see each other.
Months later, on New Year's Eve, Bobby and Vonnie are apart; Bobby in New York City hosting festivities in his nightclub, and Vonnie with her husband at a Hollywood house party. As the new year is rung in, they both seem distant to their spouses, and both have a faraway look in their eyes.