Days away from completing her first year at Miss Castwell's Institute for the Magical Instruction of Young Ladies, Changeling-born Sarah Smith might just get away with posing as an upper-class Guardian girl named Cassandra Reed.

But strange visions of a Lightbourne destroyed by Miss Morton's revenant army keep Sarah from enjoying her achievement. Plus, the Mother Book, Sarah's one secret advantage and the ultimate entrée in Guardian society, suddenly stops revealing itself to her...putting her in a precarious position with the Guild. On top of all that, her former lady's maid left Miss Castwell's, and the new hire is, well, taking some getting used to.

If it weren't for her two best friends, Alicia McCray and Ivy Cowel, who will do anything to protect her secret, Sarah doesn't know if she'll make it another year. When the three girls take summer holiday with Alicia's family (chaperoned by an exacting and very disapproving Mrs. McCray), a relaxing vacation in Scotland is the last thing they'll find.

Mrs. Winter is thrilled that Sarah is spending time with the influential McCray family, but Sarah can't help but feel that her real purpose is to find other Changeling children like her, and free them to realize their own magic. Can she find genuine satisfaction in her accomplishments when she knows there are others like her out there who need her help? Will the three girls uncover the deeply-held secrets they're looking for in the mysterious mountains of Scotland? Will the Mother Book finally start talking to her again? And will Sarah come to understand the importance of her connection with Ivy and Alicia, and the true nature of her own power...before it's too late?