Jessi knows a secret language! She learned it from Matt Braddock, the BSC's newest charge. Matt's been deaf since birth, and he uses sign language to speak. Since Jessi is 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 members of the Baby-sitters Club 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!