Jessi knows a secret language. She learned it from Matt Braddock, the Baby-Sitters' newest charge. Matt's been deaf since birth and he uses sign language to speak. Since Jessi's Matt's baby-sitter, she has to use sign language too.
Soon all the kids in Stoneybrook want to learn to sign . . . which keeps the Baby-Sitters busy. Jessi's the busiest of all: she's working on another super secret, just for Matt.
Will Jessi be able to keep the secret and pull off her special event? Of course she will - she's a member of the Baby-Sitters Club.