Cara Diana Hunter and her grandmother, Ivy Morris, realize they are being followed on their way home from the library. They duck into a church, but their pursuer follows. Cara is terrified, but her grandmother, Ivy, seems to expect this. Ivy gives Cara her special amulet and instructs her to run to the top of the church tower. She says that when she gets to the top, to clutch the amulet and fall while saying "Luster take me home" on the 12th toll of the bell. Cara does this, and ends up in a magical forest in a different world called Luster, the home of the unicorns. Cara makes several friends on her way to find the Old One, who is actually the Queen of the unicorns, in order to deliver her grandmother's message.
