Because the book is narrated by an older Scout looking back on her childhood, there are many instances of foreshadowing throughout the book.
On the first page, Scout says that her brother, Jem, broke his arm when he was almost thirteen, then adds, “I maintain that the Ewells started it all, but Jem, who was four years my senior, said it started long before that. He said it began the summer Dill came to us, when Dill first gave us the idea of making Boo Radley come out.” The phrase “it all” indicates that the story behind Jem’s accident is complicated, and the roots of the accident are open to interpretation. Scout also mentions several characters—the Ewells, Dill, and Boo Radley— who are important to the story. The next line, “if he wanted to take a broad view of the thing, it really began with Andrew Jackson,” foreshadows one of the themes of the novel, which is the South’s history, and the impossibility of untying the present from the region’s troubled past. Andrew Jackson, and Maycomb’s history in particular, are referenced again at the pageant, right before Jem and Scout are attacked, in a second instance of the narrator linking the unresolved violence of the past with the present.
Jem’s accident is also heavily foreshadowed by the events immediately preceding it the night of the Halloween pageant. Scout ends Chapter 27 by saying that although Atticus and Aunt Alexandra do not go to the Halloween pageant, “Jem said he would take me. Thus began our longest journey together.” The word “longest” has two meanings here – it describes not just physical distance, but the arduousness of the events to come. The ambiguity of the phrase increases the drama of the Halloween pageant scene, which would otherwise simply be an amusing anecdote. The ambiguity is increased by several instances foreshadowing that the children should be afraid, rather than excited, about the evening to come. Aunt Alexandra says “someone just walked over my grave” right before the children leave for the pageant. Cecil Jacobs scares them in the dark on their way to the school, and later, as they leave, someone tells them to “be careful of haints.” Scout forgets her shoes, and just as they turn back to get them, the lights in the school go out. Though there have been many scenes of Scout and Jem walking safely through Maycomb at night, these elements of foreshadowing imply that this night will be different for them.
Boo Radley’s function as a hero of the book is foreshadowed throughout. While Scout, Jem, and Dill happily believe Boo is a dangerous, deranged fiend who eats the neighborhood pets, Atticus’s reaction to their games implies Boo has been miscast in the eyes of the town. When the children suggest Boo is kept chained up in the house, Atticus says “there were other ways of turning people into ghosts.” When he catches the children trying to get Boo to come out, he says “what Mr. Radley did might seem peculiar to us, but it did not seem peculiar to him.” Atticus’s sympathetic attitude towards Boo foreshadows Boo’s role as protector of the children when he later saves them from Bob Ewell. This revelation is underscored by the evolution of Boo’s association with imagery of ghosts. In the beginning of the book, Jem and Dill describe Boo as a ghost, which they fear. Later, Scout declares “haints, Hot Steams, incantations, secret signs had vanished with our years,” foreshadowing Boo’s evolution from a fearful figure of the children’s imaginations to a real person they respect.
Bob Ewell doesn’t figure prominently in To Kill a Mockingbird until the second half of the book, but his role as the antagonist and catalyst for the climax is foreshadowed in the figure of his son, Burris. We meet Burris on Scout’s first day of school, after Scout has brought home Walter Cunningham for lunch. Walter is poor but proud, and the sympathetic portrayal of his poverty is contrasted by the depiction of Burris, who is also impoverished. Burris is dirty, covered in “cooties,” and announces he only attends school once a year, indicating his family’s lack of education. The theme of the Ewell’s ignorance will be revisited during the trial when Atticus cross-examines Burris’s sister Mayella. Another classmate tells us Burris’s “paw’s right contentious,” foreshadowing Bob Ewell’s attitude towards the Finches. We also learn that Burris is “a mean one, a hard-down mean one,” attributes he shares with his father. When the teacher tries to throw Burris out of class he insults and threatens her, foreshadowing the violence his father later enacts on Scout and Jem.