The following version of this book was used to create the guide: Kennedy, Louise. Trespasses. Riverhead Books, 2022.

In the early 1970s, in a small garrison town on the Irish border, near Belfast, an Irish woman named Cushla Lavery struggles to hold a fragile life together. She lives with her mother, Gina, who suffers from an alcohol addiction, and works part-time at a pub alongside her brother, Eamonn. Cushla also works as a schoolteacher at a Catholic elementary school, where the students are given rigorous religious training and taught to distrust Protestants. While working at the bar one night, Cushla is harassed by an Englishman and is stood up for by a man named Michael Agnew, an English barrister who is an old family friend of the Laverys. Cushla quickly develops a romantic interest in Michael, one which she attempts to hide from her employers and her family by taking up with a fellow schoolteacher of hers named Gerry Devlin. Cushla and Gerry become fast friends, and he supports her as she covets a relationship with Michael and begins furtively caring for a young boy in her class named Davy McGeown, whose mother is a Protestant. Eventually, Michael invites Cushla to spend time with his sophisticated friends and teach them Irish, and they begin a romantic relationship despite the fact that Michael is married.

Cushla and Michael's relationship becomes intense and sexual very quickly, and they begin seeing each other with more frequency. At the same time, discord arrives in the Lavery household; Eamonn and Gina begin fighting because Gina does not approve of Eamonn's wife, Marian. Cushla is left to comfort her brother and control her mother's drinking habit. Meanwhile, Cushla begins spending more time with the McGeown family, and meets Davy's older brother, Tommy, a surly young man who is initially suspicious of Cushla's charity before coming to trust her. The McGeowns' father, Seamie, is attacked by members of the RUC and becomes unable to work; Tommy elects to drop out of school in order to earn more money for the family. At the same time, cracks begin to form in Michael's relationships with his friends; one of his contemporaries, a hotheaded man named Victor, is frustrated by Michael's advocacy for Irish clients, and warns him that it could put his life at risk.

Headmaster Bradley and Father Slattery, the two men who run Cushla's school, begin to chide her for helping Davy and warn her against interacting too much with the McGeowns. In the midst of this, Michael takes Cushla on a romantic trip to Dublin, and they spend the weekend there in relative peace and harmony. When Cushla returns, however, she finds that Betty McGeown, Davy's mother, is furious with her; social services have been called on the McGeowns, and Betty believes it is Cushla's doing. When Cushla confronts Bradley, her worst fears are confirmed: her meddling has inspired the headmaster to report the family. Meanwhile, Gina's drinking becomes worse, and Michael grows distant from Cushla; one night, at his friend Penny's art show, he fails to make an appearance, and Cushla is left to interact with people whom she believes think her low-class. She begins to doubt her relationship with Michael, but continues inviting Gerry over so her family does not suspect who she has been spending time with.

Though their relationship remains strained, Cushla finds newfound respect for Michael when she realizes he is representing the son of one of his friend's housekeeper, a Mrs. Coyle, in a dangerous case against the state. This progress is stymied, however, when Cushla inadvertently runs into Michael's wife, Joanna, while she is attempting to underhandedly force a resolution between Gina and Eamonn. Although she is furious with Michael—without much justification—she agrees to meet him again. Meanwhile, Betty begins to forgive Cushla, and explains to her that Tommy is never in the house anymore. Before she gets a chance to see Michael again, Cushla learns that he has been shot dead by a member of the IRA.

A devastated Cushla moves in with Gerry, who continues to insist he has no interest in a romantic relationship with her. She confesses to Eamonn that she was sleeping with Michael and he responds with fury. Michael's friends, too, spurn Cushla at Michael's funeral. Meanwhile, it becomes apparent that Tommy McGeown is Michael's suspected murderer, something Cushla fears was her fault. She helps the McGeowns rush to safety so that they will not be killed in retribution, and fields inquiries from the police about Michael's death; they feel she is the connection between the murderer and the victim. Though Cushla is eventually exonerated, the Lavery family becomes anathema to their neighbors; their pub is bombed out and Cushla is fired by her school. However, Michael's friend, Victor, apologizes to Cushla, and tells her that she made Michael happy. Several years later, Cushla reunites with Davy in gallery displaying Penny's art, and they reconcile with one another.