Eleven-year-old Lydia Green doesn't want anything to change. She lives happily in Mulberry Glen with her mismatched family of a fairy guardian, a philosopher, and twin troublemakers known as the Zs. But now, rumors swirl about The Darkness, a powerful force that dwells in the forest Tenebrae.

Lydia knows The Darkness is nothing to be trifled with, but when a foolish choice by the Zs puts her family in danger, she must leave home and face the strange magical world of The Valleylands.

Among the shifting library shelves and new friends of her quest, Lydia uncovers more questions than answers, and the Darkness begins to creep into her mind. If she wants to save her family, she will have to be braver than ever before.