When a strange moon rises above the sister towns of Mire and Ember Hollow, Endicott Thyne is not the only witch to notice. She and her best friend Gabriela head to the woods where they encounter two other witches, Xandra and Maritza. Together, the four discover that this moon signals the Season of the Witch, a time of great magical potential that occurs every three decades. This particular Season has resurrected a dangerous figure who has not been seen in the sister towns in sixty years, and whose presence threatens the very existence of Mire and Ember Hollow. In order to uncover the identity of this stranger, they must find the hidden witch library of Mire, an archive maintained by Endicott's grandmother Dorothea Thyne until her death. But Dorothea never so much as mentioned the archive to Endicott, who is still mourning this enigmatic librarian who raised her. With a chaotic storm raging above and their magical powers suddenly bound, Endicott, Gabriela, Xandra, and Maritza will have to act fast if they are going to protect the sister towns. But they're learning that hidden pasts can be perilous, out-of-control magic can be deadly, and the Season waits for no witch.