September has longed to return to Fairyland after her first adventure there. When she finally does, she learns that the inhabitants of Fairyland have been losing their shadows—and their magic—to Fairyland Below. This underworld has a new ruler: Halloween, the Hollow Queen, who is September's shadow. As September confronts Halloween, she must navigate a world where even trusted friends like Ell, the Wyverary, and the boy Saturday may not be as they seem.