Junior high detective Sammy Keyes and her friends take a detour through a graveyard on Halloween night and find themselves in the middle of a mystery involving missing people, human skulls, and a ghoulish embalmer, while school presents its own set of tricks and treats.

When Justice Jack, a self-appointed superhero, begins trying to track down the missing Mrs. Wedgewod and some stolen cash, the older folks in Santa Martina are delighted but Sammy knows it will be up to her to really solve the mystery.