The following version of this book was used to create the guide: Tóibín, Colm. Long Island. Scribner, 2024.

Colm Tóibín's novel Long Island is set in 1979 and takes place in both Long Island, New York and Enniscorthy, Ireland. The novel is written from the third-person point of view in the past tense. For the sake of clarity, this guide uses the present tense.

In June of 1979, Eilis Fiorello is home alone when an Irishman knocks on her door. He informs her that her husband Tony Fiorello had an affair with his wife while doing a plumbing job at their home. Now his wife is pregnant. The man is so upset by the situation that he promises Eilis that he is going to leave the baby on her doorstep after the birth.

Shocked and confused, Eilis spends the next several days in a daze. She starts spending more time working at the garage where she does the books for the family business in order to avoid Tony. She also wants to avoid Tony's family. Tony's parents, brothers, and sisters-in-law all live in the same cul-de-sac in Lindenhurst where Tony and Eilis live with their children Rosella and Larry Fiorello. Eilis has no privacy and fears that her extended family will discover the baby issue. One day, she travels to Manhattan to see Tony's youngest brother Frank Fiorello. He is the only son who does not live in Lindenhurst. Because Frank is a lawyer and he and Eilis have always had an understanding, Eilis asks him for advice about the baby. Frank informs her that his mother Francesca Fiorello already knows about the situation and plans to have Tony adopt it, after which she will raise the baby in her home.

Eilis has confrontations with both Tony and Francesca. She informs them that she will not adopt the baby or welcome it into her family. Neither Tony nor Francesca seems to care. Disgusted and trapped, Eilis decides to leave town and visit her mother in Enniscorthy for the summer.

Eilis's former best friend Nancy Sheridan is shocked when Eilis returns to town. She has not been back since her sister Rose's funeral 20 years prior. Seeing her again, Nancy feels immediately self-conscious. Eilis is thin and stylish and has maintained her youthful appearance. Meanwhile, Nancy has put on weight since her husband George Sheridan's death five years prior and smells like fish from running her chip shop. Nancy is also seeing Eilis former love Jim Farrell in secret. Over the following days, she worries that Jim and Eilis might rekindle their romance. To secure her future with Jim, Nancy starts making plans to marry him in Rome in the spring and to build a house with him in the country thereafter.

Jim realizes that he is still in love with Eilis as soon as they see each other again. They start meeting in private. Meanwhile, Jim tells Eilis nothing about his secret engagement to Nancy. He does not want to hurt Nancy but feels powerless to let Eilis go again. Twenty years prior, Eilis and Jim fell in love but Eilis broke Jim's heart when she returned to Brooklyn without notice. A few months later, Jim discovered that Eilis was married to an Italian man in Brooklyn.

Eilis receives a letter informing her of Tony's baby's birth. Furious, Eilis decides to divorce him and be with Jim. She and Jim meet in private and make plans for their future. Jim agrees to follow her to New York and make a life for himself while she handles her affairs. After making these arrangements, they kiss on the beach and promise to see each other before Eilis returns to New York. Meanwhile, Nancy is crouching on a bluff and spying on Jim and Eilis. After seeing them together, she races home and dons her old engagement ring. She tells everyone in town that she and Jim are getting married. When Eilis discovers the news, she confronts Jim. He admits that he and Nancy are engaged but that he still wants to be with her. Eilis leaves his house without saying anything. Afterward, Jim sits alone and tells himself that he will resolve the issue in the morning.