Kristy Thomas is the protagonist and narrator of the first book in the Baby-Sitters Club series. The club begins from an idea that Kristy has at the beginning of seventh grade, and she is very proud of this fact. It is a hot day at school, and when the day finally ends, Kristy jumps out of her seat and yells for joy, which leads to her teacher reprimanding her. He asks her to write an essay on the word “decorum.” Kristy admits that she can be impulsive, which can sometimes lead to trouble. Kristy has two older brothers, Charlie and Sam, and one younger brother, David Michael, who is six. They all live with their mother, who divorced their father a few years before.

Kristy’s best friend, Mary Anne, lives next door to her. While Kristy is outgoing and outspoken, Mary Anne is quiet and somewhat reserved, except around her closest friends. Mary Anne’s mother died, and she has no siblings; her father, Mr. Spier, is extremely strict. Mary Anne and Kristy live across the street from their friend Claudia, who is passionate about art and seems to be maturing faster than them.