Brooklyn is set in Enniscorthy, Ireland in the 1950s. It follows the life of a young woman named Eilis Lacey. When the story opens, Eilis is struggling to find work, leaving her sister Rose to support Eilis and their mother by herself. When Eilis finally does find work, it is a part-time job at a local grocery store owned by the notoriously snobby Miss Kelly, who looks down on her and her family. Eilis is smart, and dreams of being a bookkeeper like her sister, but there are simply no opportunities in the town, and economic and social advancement seems next to impossible.
Her friend, Nancy Byrne, hopes to achieve a better life by marrying a man named George Sheridan, who is well-respected and relatively wealthy in their community. But Eilis herself seems to have little hope of bettering her situation through marriage, especially after she is snubbed by the relatively wealthy Jim Farrell at a Friday night dance.
Her sister Rose devises a solution. She arranges to send Eilis to America under the care and guidance of a young Irish priest named Father Flood. He will find her a job and a place to board, and help to integrate her into the Irish immigrant community in Brooklyn. Eilis is apprehensive and reluctant to leave behind the only home she has ever known. But she also sees what Rose sees: there is no future for her in Enniscorthy. So, she agrees to make the long and terrifying trip across the Atlantic.
The voyage starts miserably for Eilis, as she struggles with seasickness and the unkindness of her fellow passengers. But she makes it through with the help of a more seasoned transatlantic traveler named Georgina, who also helps her to prepare to pass through immigration and present herself in this new country. In Brooklyn, she is met by Father Flood, who finds a room for her in a boarding house run by a woman named Mrs. Kehoe, who hosts several other young Irish women. Father Flood arranges for her to work at a department store called Bartocci’s. It is a sales job, but it pays well, and the store will likely hire her as a bookkeeper later on if she continues her studies.
The change is overwhelming, and once the excitement wears off, Eilis finds herself more and more depressed. Her co-workers cannot help but take notice. Miss Fortini, her supervisor, tells her that she must be more cheerful and friendly towards the customers, or risk losing her job. She gives her the rest of the day off, and suggests she talk to Father Flood. Father Flood explains that what she is experiencing is simple homesickness, and that it will get easier with time. He enrolls her in a bookkeeping course to keep her busy and distract from her loneliness. He invites her to spend the holidays serving meals to the poor at the church in an effort to keep her involved in the community.
His efforts pay off, and Eilis gradually feels more at home in Brooklyn, but life in America is not without its challenges. For one thing, she must navigate the issue of race, which was hardly a problem in the homogenous Enniscorthy. When Bartocci’s begins selling darker-colored stockings for black women, Eilis is chosen to man the sales counter, and she experiences firsthand the tension this causes among her coworkers and customers alike. Even her fellow boarders at Mrs. Kehoe’s are judgmental of the decision, and of Eilis’s role serving black customers. Eilis, in spite of her own ignorance of the issue, is forced to take a side. She continues working at the counter for black women, and silences her housemates when they make racist remarks.
Still, she is very much ignorant about the history of race in America, or in the broader world. One of her favorite teachers in her bookkeeping course is a Jewish man named Joshua Rosenblum. She learns from a local bookshop owner that his family had all been murdered by the Germans. Eilis asks if he is referring to the war, and when he explains that he means the Holocaust, she seems not to recognize the term. Even though she is well-intentioned, she struggles to navigate this new diversity. Even her home life introduces new stresses.
At Mrs. Kehoe’s, the boarders are split into two rough factions: the young, Americanized Patty and Diana, and the older, traditional Miss McAdams and Sheila. Eilis, while close to none of the girls, is constantly caught between them, especially when Father Flood starts throwing dances at the parish. She is unsure whether to go with the stiff, prim Sheila and Miss McAdams, or the silly, wild Patty and Diana. She attends once with the older women, and they are so unpleasant that she vows never to do so again. The next week, she spends more time with Diana and Patty instead, but a chance meeting spares her from making any more decided alliance.
At one of the dances, she meets a young man named Tony. He asks her to dance, and though Eilis initially only intends to spend one or two dances with him, she stays with him the whole night, and even allows him to walk her home. His easy confidence and playful smile charm her, and he is a perfect gentleman. Soon, they are attending every dance together, and going to the movies every weekend. Eventually, Eilis even lets Tony walk her home from class during the week. She and Tony gradually get to know each other. Tony tells her about his Italian family, his work as a plumber, and his family. He is open and earnest, and makes Eilis feel like she can be open, too. She tells him about her bookkeeping course, and her struggles with homesickness upon moving to Brooklyn.
She eventually feels seriously enough about Tony that she writes to Rose about him, though still not their mother. Rose enlists Father Flood to get to know him, and Tony makes a great impression on the priest. But Tony takes things even further. He tells her he loves her, but she does not know how to answer, and so she says nothing. When he later makes a comment about their future children, she realizes that they are not on the same page about the relationship, and that Tony is moving too quickly for her. She begins to pull away, spending some time on her own. This clearly hurts Tony, but he still shows up to pick her up from class. As Eilis watches him from the window, and considers all the things she likes about him, she knows she must make a decision one way or the other. In a decisive moment, she tells Tony, fumblingly, that if he told her he loved her again she would say she loved him too. He is thrilled, literally jumping up and down. But she is still anxious, asking him not to talk about their children, or push her too far.
Some time later, Eilis finally agrees to meet Tony’s family. They have dinner in his cramped three-room apartment, where he lives with his parents and three brothers. His youngest brother, Frank, announces at dinner that they do not like Irish people, because Maurice had been beaten by some Irish boys, and the police, who were also Irish, had done nothing. Eilis is more amused than hurt, especially after everyone at the table scolds Frank and assures her they do not hate Irish people. The conversation gradually becomes more comfortable, and Tony’s family seems open-minded and kind. Still, when Tony is called away to fix a plumbing problem during dinner, Eilis is uncomfortable making conversation with the family alone. She is relieved to find an ally in Frank. Though dejected after being scolded, he perks right up to tell her about Tony’s ex-girlfriend. Though this is clearly a taboo topic, Eilis does not tell the rest of the family, and so wins his affection.
During that summer, Tony invites Eilis to Coney Island, where they can go to the beach. This invitation makes her anxious, as she has no suitable bathing suit and this will be the most of her body Tony has ever seen. Miss Fortini volunteers to help her choose an American-style swimsuit. Eilis tries some on at Bartocci’s after work, and Miss Fortini sizes her up, advising her to shave her bikini line and watch her figure. Though Eilis appreciates the help, she cannot help but notice that Miss Fortini makes every excuse to touch her, and that her eyes linger on Eilis’s body in more than a casual way.
On the day of the Coney Island trip, the beach is packed, and Eilis and Tony have to carve out a place on the sand. They spend much of the day in the water, where they hold each other closely under the waves. This is clearly an exciting experience for them, as they have never seen each other less than fully clothed. Tony even gets an erection as he holds Eilis, and his total lack of shame make her feel amused and even more affectionate towards him.
The summer goes on, and everyone is swept up in baseball season, especially Tony. Tony brings Eilis to a Dodgers game with him and his three brothers, and though she does not understand the game, she is charmed by his passion and excitement.
By Christmas time, Tony takes another important step in their relationship. He tells her that he and his brothers have bought land on Long Island that they plan to develop. One house will be for his parents, and three they will sell, but the last will be for him and Eilis, if she wants it. He explains how he and his brothers will go into business developing houses, and that in this way, he will be able to give her a better life. Eilis knows the significance of Tony laying out their future like this, and she is touched, but she makes no response aside from holding him close.
Eilis’s happiness is soon disrupted by devastating news. Her sister Rose has died in her sleep of a heart condition which she had kept a secret from her family. Eilis is heartbroken. She leans on Tony much in this difficult time, and his support of her in her grief makes them feel closer than ever.
Eilis feels so close to him that she even allows him to stay the night at her apartment, in spite of the possibility of being turned out by Mrs. Kehoe. In her room, they have sex for the first time, and the experience is surprisingly painful for Eilis. Still, she enjoys Tony’s desire for her, and the new closeness it brings them. It puts her in a difficult position with Mrs. Kehoe and Father Flood, however, who find out about Tony staying the night, but they ultimately let the matter go.
Soon, she receives a letter from her brother Jack, who attended the funeral. He tells her that their mother is suffering more than she is willing to admit to Eilis, and asks her to visit home to spend time with their mother and help lessen her grief and loneliness. Eilis, distraught, immediately shows Tony the letter, who pales. He understands her need to go home, but he asks her to marry him before she goes, explaining that she will not come back otherwise. He says that they can have a more public ceremony when Eilis returns. Eilis is hesitant at first, but she eventually agrees to this arrangement, and the two get married in secret.
Once back in Ireland, Eilis finds it difficult to readjust to life in Enniscorthy. Her mother monopolizes her time, enlisting her to write countless thank-you notes, tend to the flowers on Rose’s grave, and clean out Rose’s things. Her mother asks no questions about her life in Brooklyn, and urges her to keep many of Rose’s things, as if she is in denial of Eilis ever returning to America. Eilis, in turn, finds it hard to broach the subject, and especially to tell her mother about Tony. Her mother’s intentions become clear when Eilis finds out that she has promised that Eilis will attend Nancy’s wedding, which is after Eilis is supposed to depart. But, unwilling to tell her family and friends about Tony, she hardly has a reason to refuse. Eilis ultimately decides to extend her stay in order to attend the wedding, and tell her mother about Tony in a letter upon her return to Brooklyn.
In the meantime, she spends time with friends. One day, she makes beach plans with Nancy and George, only to discover that Nancy has invited Jim Farrell to come with them. At first she is angry at Nancy, both for inviting him and for not telling her. But it is clear that Jim has a new interest in her, and makes every possible effort to win her good opinion. She softens towards him throughout the day, and even agrees to go out with them again. The next week, they go to a deserted beach of Nancy’s choosing, clearly calculated to allow Jim and Eilis to be alone together. Eilis decides to go along with what she sees as a harmless flirtation, but it quickly becomes something more. She goes swimming with Jim, which she had sworn to herself that she would not do, and she allows him to embrace her in a photo they take together. Later on that night, when they all go to a dance, she dances with him, and finally even allows him to kiss her.
They continue spending time together like this until the wedding, when Jim picks up Eilis and her mother and drives them to the celebration. By now, everyone seems to see them as a couple, including Eilis’s mother, who is ecstatic about the match. Eilis is forced to confront the fact that her marriage was a mistake, but one that she cannot easily extricate herself from. When Jim tells her that he wants to get engaged before she returns to America, this is only thrown into sharper relief. She knows that however she might feel about Jim, he will never accept that she is already married, and will need to get a divorce in order to be with him. She leaves his question unanswered, pushes everything out of her mind, until an unexpected event makes her face facts.
Miss Kelly calls her into her apartment one afternoon, and tells her that she has heard from her cousin Madge Kehoe that Eilis is already married. Though Eilis admits nothing, she is rattled by Miss Kelly’s threat to expose her to the whole town.
She knows that she cannot keep up the charade any longer. She books a ticket to Brooklyn, and tells her mother the dreaded news. Her mother is clearly devastated, but she attempts to hide her feelings and remain positive. When her mother asks her whether she would be returning to Brooklyn had she not been married, Eilis can only say that she does not know. Eilis can see that she has hurt her relationship with her mother, especially when she insists on saying goodbye now and going to bed early. But she can find no words to fix what she has done, and instead packs for the next day.
On the way to the station, she leaves a note for Jim Farrell in his mailbox, with a promise to explain everything in a letter. She thinks about how he will feel once she is gone, how she will fade from his memory. She reflects on the fact that though her return to Brooklyn will come to mean less and less to him, it will come to mean more and more to her.