Thirteen-year-old Byron ("By") is a "juvenile delinquent" in the terminology of the times and the older brother to the main character, Kenny. By cultivates a cool, tough-guy demeanor, and he is in active rebellion against his parents. They are so fed up with and worried about him that they finally make plans for him to spend the summer with his grandmother in Birmingham, Alabama.
Kenny is bullied by By, but he also admires his daring and sense of humor, so he has mixed emotions about his enigmatic older brother. By's "fantastic" escapades attract Kenny but also frighten him.
By is a well-rounded character. For example, he wants to change and meet his parents's expectations, especially as they get increasingly upset with him, but he also finds himself allured by trouble. His mother threatens to burn him if he keeps setting fires, but By, though well-meaning at heart, has difficulty following her demands.
Beneath his tough-guy facade, By is sensitive and confused, hiding his insecurities under bravado. He does care about other people and living creatures, but he's going through an adolescent phase where he has to sort his identity out. It isn't easy to be thirteen, especially as a black young man in a racist country in 1963.