A traveling carnival is on its way to Sweet valley, and Jessica and Elizabeth Wakefield can't wait to ride the roller coaster, have their fortunes told, and try their luck at the games. But when they get there some odd things happen to the twins. A fortune-teller warns Jessica to stay away from the carnival. And a mysterious girl named Clair seems to appear out of nowhere and suddenly becomes best friends with Elizabeth. Elizabeth is strangely drawn to Claire. She begins to ignore her friends, her chores, and even her sister to spend time with her new friend. It's as if she's under an evil spell...a spell no one, not even Jessica, can break. And if her twin is in danger, how can Jessica help her?