In Hallahem, a secret city beneath a mountain, lives twelve-year old Torun, of the Vitter people. Unknown to her, she is a changeling, and in fact human. One day Torun overhears a conversation, realizing that Hallahem is being threatened by modern civilization. She learns there is another girl who can help them, a girl that could have been her. She soon meets Tilda, also a changeling, but a Vitter living with humans. Together they have to face challenges of mystery and dangers and soon Hallahem’s future rests on their shoulders.