Copyright Paperback Collection (Library of Congress)

"Claudia's not worried when she hears her newest baby-sitting charge, Betsy Sobak, is a great practical joker. After all, how much harm can one little girl do? Plenty. Claudia breaks her leg as a result of one of Betsy's mean jokes... and now she's talking about quitting the club. Baby-sitting, she says, is just too dangerous. Kristy thinks Betsy needs to be taught a lesson. She also thinks the Baby-sitters are just the ones to do it. Watch out, Betsy...