Cal McCluskey and his father, Shamie, are the last Catholic family living in their neighborhood in Belfast, Northern Ireland, during "The Troubles." Shamie works in an abattoir, a slaughterhouse, and he wants Cal to work with him, but the work turns Cal's stomach. Cal's mother died several years ago, and he does not have good self-esteem or a good relationship with Shamie. One day, he goes to the library and learns that the librarian's name is Marcella, and he realizes that she is the wife of a Loyalist cop, Robert Morton, whose murder he participated in a year earlier. Cal becomes obsessed with her.
Crilly and Skeffington approach Cal about being their getaway driver. Crilly was an old school-mate of Cal's. He is unintelligent and violent. Skeffington is about ten years older than they are, and he is much more of a ringleader. Cal agrees to drive, but only if it's to get money—he doesn't want to participate in any violent crimes, and he experiences terrible guilt as a result of the one he was involved in.
Cal and Shamie are threatened constantly on account of their religion, and, eventually, their house is burned down by Loyalist Protestants (or Orangemen, as they are often referred to in the novel). Cal has frequent nightmares. He gets a job at the Morton house, the home of Robert's mother, father, widow, and daughter. When his house is burned down, he moves into a cottage at the Morton residence, and when Mrs. Morton finds out, she actually allows him to go on living there, loaning him furniture to make the place habitable. Meanwhile, Cal gets closer and closer to Marcella. No one suspects his involvement in Robert Morton's murder, and his guilt increases as their relationship progresses. They eventually sleep together, giving Cal the thing he wants most—her—as well as increasing his guilt exponentially.
Cal has to hide from Crilly and Skeffington because he no longer wants to participate in their crimes. When Crilly does finally spot him in the library, Cal must accompany him to Skeffington's house to discuss his "getting out." The police show up, catching Crilly and Skeffington, but Cal gets away. He knows it's only a matter of time before the police come for him, and they do in the end.