Cassandra "Cassie" Bristow has made it to her senior year. Finally being permitted to go to a public school (as opposed to her home schooling for years), Cassie is ready to live as a normal teenager. At first, she thinks she's got it; she makes new friends, figures out her class schedule with ease, and even catches the eye of Christopher Lyons, the star of the football team. But when a mysterious new girl named Jessica shows instant interest in her, Cassie wonders if she's as normal as she thinks. She swears she knows Jessica from somewhere, even if she can't remember. And so doesn't Christopher. The two hold a dark secret about Cassie that will change her world and force her to make a choice. But when a shadow from Christopher's past arrives, Cassie realizes she could end up destroying the world. And all it would take is one wrong move.