To restore her family’s honor and status, Hyacintha agreed to become the warden of a secluded castle. She took an oath and used magical seals. But soon it turned out that this ominous place needed more than a mere caretaker—it required strict supervision. Now she is responsible for a monster locked in the boundary between worlds, and her life is the price. What’s more, Hyacintha brought a secret to Grabon. When it becomes known, another prisoner may appear in the castle…