You can find a full summary of the novel by visiting the link below, but here is a brief synopsis:
The setting is rural Maycomb, Alabama at the time is the mid 1930s. Scout and Atticus Finch are the children of Atticus, the town's lawyer and one of the few non-prejudiced people in town. Atticus takes on the case of a black man who is accused of raping a white woman. It seems like a case that should not be hard to win, especially since the prosecutions key witness' testimony falls apart on the stand. But hatred wins out over justice. The two children realize that innocence is not always enough, but doing the right thing is mandatory.
A subplot of the story also follows the lines of learning tolerance. Scout, Jem, and their friend Dill, are intrigued by a local resident named Boo Radley. He is the subject of teasing and conjecture; the man never leaves his home. He is given all sorts of characteristics that have nothing to do with his true nature. The children learn, after they get to know him, that this prejudice is also unfounded.