It is in essence the coming-of-age story (told in a first person account) of the main character, six-year-old Scout Finch, who lives with her older brother Jem and their widowed father Atticus, a lawyer, in the sleepy little town of Maycomb, Alabama. After befriending a boy named Dill, who has come to live in their neighborhood for the summer, the siblings and Dill act out stories together, where they eventually become fascinated with the Radley Place, a house on their street, where it is said that Arthur (nicknamed Boo) Radley, has lived for years without venturing outside. When they start making fun of Boo, Atticus utters one of the great quotes from the book: "You never really understand a person until you consider things from his point of view . . . until you climb into his skin and walk around in it."
This first plot, where the kids are scheming ways to get a peek at the town bogeyman, very slowly converges with the other plot, in which their father gets appointed to defend a black man, Tom Robinson, who is falsely accused of raping a white woman. While Atticus defends him brilliantly in court, he suspects he will lose the case. And that is what happens, when Robinson is convicted by an all-white jury and later shot during a prison break attempt. Despite his challenges, Atticus faces up to them just the same, at one point heroically stepping between his client and a lynch mob.
The plots eventually merge, when the father of the alleged rape victim, a town drunk named Bob Ewell, whose "reputation" was ruined during the court proceedings, vows revenge to the Finch family and ends up attacking the children on their walk home at night from a Halloween pageant. In the struggle, Jem's arm is broken but Boo Radley comes to their rescue, in which Bob Ewell ends up dead. The sheriff and Atticus argue about whether the children should be held responsible but Atticus eventually accepts the sheriff's story that Ewell simply fell on his own knife. After walking Boo home and saying good-bye, Scout remembers her father's words and imagines life from Boo's perspective.
On the face of it, the book portrays society in a small town in the U.S. South of the 1930s, where racism is part of the very fabric of society. On a deeper level, though, the book narrates the two themes of tolerance and justice. It is these ideas - personified in Atticus Finch, who uniquely understands that people are both good and evil and that one can understand evil without losing faith in the human capacity for goodness by treating others with sympathy and trying to see life from their perspective - that makes this a charming and ultimately uplifting read despite the considerable darkness of its plot (typical for a Southern Gothic novel).
"To Kill A Mockingbird" ultimately asks us to adhere to the moral imperative to protect the vulnerable even though it might mean being distanced, hated or disenfranchised from those around us. To that end, it uses the metaphor of the mockingbird as good and innocents that can be easily destroyed by evil unless one watches out over them. To underscore this point, I end with the exchange from chapter 10, from which the book also drew its title:
Remember it’s a sin to kill a mockingbird.” That was the only time I ever heard Atticus say it was a sin to do something, and I asked Miss Maudie about it.
“Your father’s right,” she said. “Mockingbirds don’t do one thing but make music for us to enjoy . . . but sing their hearts out for us. That’s why it’s a sin to kill a mockingbird.”