Stacey can't wait to get involved in the plans for Stoneybrook Middle School's Mischief Night Masquerade, but someone is trying to sabotage the event and Stacey and her friends in the Baby-Sitters Club are determined to find out why.
The members of the Babysitters Club sign up to help with the reopening of a country club and set out to solve a twenty-year-old mystery about a secret society that supposedly operated out of the building.
Luke Martinez, one of the Babysitter's newest charges, has a secret that is making him very unhappy, and the BSC members believe it must have something to do with the mysterious fire at his house and the plans of a mean developer who seems set on destroying Stoneybrook.
The Hatts, owners of the spooky old Stoneybrook lighthouse, come to stay at Claudia's house, but it soon becomes clear that someone, or something, wants them to leave town and the Baby-sitters are determined to figure out who and why.
