In To Kill a Mockingbird by Harper Lee the rape case in which Atticus Finch agrees to defend Tom Robinson is a pivotal part of the plot. Tom Robinson, a black man, has been accused of raping Mayella Ewell. The book is set in Alabama before the Civil Rights Act of 1964, and in a period where racism and lynching were still not condemned by many white people. 

Tom Robinson, a black laborer, has helped Mayella with some of her chores. This violates the social norms of racial segregation, and he is resented by Ewell for that act. Although Atticus Finch conclusively proves that Robinson could not have been the rapist because his left arm is disabled; Ewell though is left-handed. Despite this, Robinson is first convicted and then killed. 

Mr. Ewell lies during the trial and consistently insists that Robinson is guilty despite forensic evidence to the contrary. He is furious at the Finch family because of Atticus' defense of Robinson (and perhaps because he is covering up abuse of his own daughter).