On the storm-lashed shores of SandIsle, a legacy of secrets is about to break. When Maggie’s twins vanish into the island’s dark heart, a desperate group of women must confront the unthinkable. From a cryptic treehouse to the hollows of a subterranean hell, they track a monster born of a forbidden ritual. As the “Shadow Book” reveals its final, bloody truth, the lines between medicine and magic blur. On SandIsle, some spirits never leave – and some debts are paid in blood.