Back in Fairyland at last, September discovers a chilling truth: shadows—and magic—are vanishing into the mysterious depths of Fairyland Below.

In this strange underworld, her own shadow has risen as Halloween, the Hollow Queen. With trusted friends like Ell, the Wyverary, and the boy Saturday not quite as they seem, September must navigate this shadowy realm to reclaim what's been lost.

Will she confront the darkness within and restore balance, or will the Hollow Queen's reign consume all she holds dear?