After 13-year-old Marnie fights with her mom about not being allowed to celebrate Halloween for unknown reasons, her grandmother, who she rarely gets to see, arrives for her annual visit on Halloween night. But when Marnie overhears her grandmother and mother talking about the fact that she's a witch, she and her siblings follow their grandmother to her bus headed for Halloweentown. After their arrival, they show up at their grandmother's house and try and help her solve the mysterious disappearances that have happened recently. They come to find that Halloweentown's mayor, Kalabar, is responsible, and they use their powers (along with their mother's, who eventually comes to her senses) to defeat him.
