Brighton Beach Memoirs begins in September 1937, within the Jerome household. The Jeromes reside in a lower-middle-class area of Brighton Beach, New York. It is around 6:30 in the evening, and fourteen-year-old Eugene Morris Jerome is outside, engaged in a semi-imaginary game of baseball. When his ball strikes the house, his Aunt Blanche Morton develops a headache. Eugene's mother, Kate, shouts for him to cease playing and come inside. Eugene reluctantly complies. He informs the audience of his aspirations to become either a professional baseball player or a writer. Sent upstairs, he starts writing in his journal.

Eugene explains to the audience that his Aunt Blanche and her two daughters, Nora and Laurie, live with his family because Blanche's husband passed away from cancer six years earlier. Eugene's father, Jack, has been working two jobs for three and a half years to support everyone. Eugene's writing is interrupted when Kate demands he come down to set the table instead of Laurie. Laurie has a heart condition, and Eugene grumbles about having to do everything because of his cousin's illness.

As Eugene sets the table, sixteen-year-old Nora rushes in, brimming with excitement. She has been given an opportunity to audition for a dancing role in a Broadway show. Nora mentions that the producer assured her the part if her mother consents. Blanche hesitates because accepting the role would mean Nora dropping out of school. However, Nora argues that she could financially support Blanche and Laurie with the job. Unable to decide, Blanche opts to leave the decision to Jack when he returns.

Eugene's mother sends him to the store, and Nora and Laurie converse in their room. They talk about their deceased father and resolve to save all their money to buy a house for their mother. When Eugene returns, his older brother Stanley is waiting for him. Stanley reveals that he was fired for defending a coworker. To get his job back, he must apologize to his boss. Stanley wants to stand by his principles, but the family urgently needs the income. He decides to discuss it with their father.

A weary-looking Jack Jerome arrives home, carrying several large boxes filled with noise makers and party favors. His second job involved selling these items to hotels and nightclubs, but the business closed that day, leaving him unemployed. Jack worries about supporting the large family. At dinner, the atmosphere is tense. Jack suggests that Stanley ask his boss for a raise. Laurie mentions Nora's audition offer, much to Nora's embarrassment. After dinner, Nora insists on discussing the audition with Jack, despite her mother's attempts to stop her. Jack offers his advice as they walk down to the beach.

Meanwhile, Stanley and Eugene are chatting in their room. Eugene shares an erotic dream he had, and Stanley informs him that it was a wet dream. Eugene then asks Stanley about puberty and girls, particularly their cousin Nora, but Stanley is preoccupied with his job issues.

Downstairs, Kate and Blanche have a conversation. Kate tries to persuade Blanche to attend a party hosted by Jack's company next week, but Blanche reveals she has a date with Frank Murphy, a man who lives across the street with his mother. Nora and Jack return, and Nora urges her mother to make a decision. Like Jack, Blanche believes Nora should finish high school. This angers Nora, causing her to storm upstairs.

Jack is becoming increasingly tired, and Kate wants him to go to bed. Stanley shows up and asks to speak with his father. Stanley explains the situation to Jack, who understands his predicament. Stanley decides to write an apology letter. He hires Eugene to write the letter in exchange for a detailed account of the time Stanley saw Nora naked in the shower.