Scout Finch, six years old, lives with her older brother, Jem, and her widowed father, Atticus, in the small town of Maycomb, Alabama, during the Great Depression. Atticus works long days as a lawyer and earns enough money to keep the family out of poverty. Calpurnia, the family's black chef, assists him with the children's upbringing. Scout, on the other hand, thinks Calpurnia is despotic and that she prefers Jem to Scout.
Atticus defends a 25-year-old black man in a court case against the Ewells. Mayella Ewell, according to Bob Ewell, was raped by Tom. However, Tom is a good man, a church member, and a married father of three, as well as a beloved member of Maycomb's black community and a devoted employee of Mr. Deas. Atticus argues that Tom, who lost his left arm as a boy after getting it caught in a cotton gin and was unable to use it, couldn't have strangled and beaten a woman with only one arm. Tom describes the terrible situation Mayella put him in when she hugged and kissed him in his testimony. He couldn't have pushed her away or forcibly removed himself because he was a black man—though fleeing was his only option, it made him appear as if he was guilty of something more.
The community's pervasive racism means that Tom has little chance of a fair trial. Despite knowing he cannot win the trial—a matter his children don't understand—Atticus knows he must nonetheless defend Tom. Throughout the trial, Scout and Jem learn valuable lessons about justice, prejudice, and what is right.
Mayella's father, who has physically and sexually abused her, appears as the real criminal during the trial. Ewell is outraged that Atticus has drawn the community's attention to him, and he publically threatens Atticus despite Tom's guilty conviction.
Mr. Ewell, drunk and enraged, ambushes Jem and Scout in the dark shadows of the trees just outside the Radley house, leaving them defenseless. Scout can't see much of what happens, but she hears Jem scream in pain as the scuffle intensifies. That's when she notices the silhouette of a second man, not the assailant, carrying Jem toward the Finch house.
Scout realizes that the man who saved them, and killed Ewell, was Boo Radley. She tells Atticus that punishing Boo would be like killing a mockingbird. Scout walks Boo home, after leading Boo to say goodnight to Jem, who’s unconscious. As Scout stands on the Radley porch, seeing the world as Boo must see it and reflects on the experiences of her last few summers. She begins to understand that Boo truly was their neighbor and cared about “his children,” Scout, Jem, and Dill.