Eilis Lacey lives in a small town in Ireland with her mother and older sister Rose. She lives a pretty boring existence, hanging at home and going to school to become a bookkeeper.
Everything changes when Rose introduces her to Father Flood, a priest who wants to help Eilis immigrate to America to find work. Eilis is hesitant—naturally—but she doesn't really have a choice in the matter. Fast-forward a few weeks and suddenly our young heroine is on an ocean liner heading straight towards big city Brooklyn.
There she moves into a boardinghouse run by an Irishwoman named Mrs. Kehoe and gets a job at Bartocci's Department Store. Everything is pretty cool and exciting, but Eilis gets slammed by intense feelings of homesickness after receiving her first letters from the fam. Luckily, Father Flood saves the day by inviting Eilis to serve Christmas dinner at his parish, which makes Eilis feel connected to her Irish roots.
Of course, it also helps that she meets a fella named Tony. Tony is an Italian-American charmer, and he and Eilis quickly spark a romance. Although Eilis digs him, she's not moving anywhere near as fast as he is: he tells her that he loves her immediately and frequently alludes to them getting married.
That's when Eilis gets devastating news: Rose died in her sleep. This sends Eilis into a whirlwind of emotions, leading her to sleep with Tony for the first time, and then deciding to go back to Ireland for a month to take care of her mom. When Tony hears about this, he begs her to marry him before she goes and—shocker—she agrees. They tie the knot in a courtroom.
Ireland is weird. Eilis' mom keeps on treating her like Rose, dressing her in her older sister's clothes and even getting her a temp job at her old office. Eilis still hasn't revealed her marriage, however. This ends up complicating things a great deal, as Eilis sparks a romance with Jim Farrell, a kid she had met before moving to Brooklyn. This relationship gets pretty serious too: Jim asks her to get engaged so she doesn't return to Brooklyn.
Eilis is torn, but the decision is taken out of her hands when Miss Kelly—her former boss in Ireland—reveals that she knows Mrs. Kehoe, and that Mrs. Kehoe told her about Eilis' marriage. Knowing that this would cause a massive scandal, Eilis comes clean to her mom, writes an apology letter to Jim, and hops on a train that will take her to a Brooklyn-bound boat.