The second book of the Deptford Histories brings readers into a time of magic and darkness, when a series of dark wars between the bats and the squirrels has raged for years. The squirrel leader, the Starwife, has been betrayed and poisoned. As she lies dying, she summons a falcon to take the magic Silver Acorn to safety.

Far away in another corner of the land, the squirrel maiden Ysabelle is unaware of the devastating events. But she rescues the Silver Acorn and embarks on a nightmarish journey to return it. Along the way, she meets Vespertilio, a young bat who has dreamed of participating in the battle against the squirrels. In the course of their journey together, they discover that the only way to battle the evil power that threatens their lands is to work together.