When her parents decide to get a divorce, Stacey must choose between staying in New York with her father or moving back to Stoneybrook with her mother.
Stacey invites her Baby-sitters Club friends to New York City for a long weekend full of activities but, much to her dismay, nothing turns out exactly as planned.
While helping Stacey move back into her house in Stoneybrook, Mallory and Claudia find an old trunk containing the diary of a girl who lived in Stacey's house in the 1890's.
Kristy and the Baby-sitters Club plan a huge outing as a Mother's Day surprise for their clients, while Kristy's mother and stepfather have a surprise of their own in store for their family.
Eleven-year-old Mallory is excited when it looks like the eighth-grade girls will invite her to join their Baby-sitters Club and she might become best friends with the new African-American girl in the neighborhood, but the club members have to learn some lessons in fairness first.
The members of the Baby-sitters Club think they can handle a young practical joker, but when one of her tricks causes Claudia to break her leg, the girls know they must teach their new charge a lesson.