Claudia's sister Janine is too busy being smart to be nice to anyone—even their grandmother Mimi. But Claudia doesn't have to see Janine too much this summer since the Baby-Sitter's Club is starting a new play group. It's going to be so much fun! But then Mimi has a stroke and the whole summer changes. Now Claudia is 'Mimi-sitting' and Janine is no help at all. How can the Kishi sisters get along when Janine is always so mean?