It is set in the fictional town of Maycomb, Alabama, during the Great Depression (1929–39)
The protagonist is Jean Louise (“Scout”) Finch, an intelligent though the unconventional girl who ages from six to nine years old during the course of the novel.
She is raised with her brother, Jeremy Atticus (“Jem”), by their widowed father, Atticus Finch. He is a prominent lawyer who encourages his children to be empathetic and just.
He notably tells them that it is “a sin to kill a mockingbird,” alluding to the fact that the birds are innocent and harmless.
When Tom Robinson, one of the town’s Black residents, is falsely accused of raping Mayella Ewell, a white woman, Atticus agrees to defend him despite threats from the community.
Although Atticus presents a defense that gives a more plausible interpretation of the evidence—that Mayella was attacked by her father, Bob Ewell—Tom is convicted, and he is later killed while trying to escape custody. A character compares his death to “the senseless slaughter of songbirds.”
The children, meanwhile, play out their own miniaturized drama. Scout and Jem become especially interested in the town recluse, Arthur (“Boo”) Radley, who interacts with them by leaving them small gifts in a tree.
On Halloween, when Bob Ewell tries to attack Scout and Jem, Boo intervenes and saves them. Boo ultimately kills Ewell. The sheriff, however, decides to tell the community that Ewell’s death was an accident.
Scout agrees, noting that to do otherwise would be “sort of like shootin’ a mockingbird.”