When April and her twin brother, Will, gather in the Bone Church near Prague with the other apprentices of the alchemical guild on the night of the eleventh new moon of the year, April makes the unexpected acquaintance of Jack Rosier, a young alchemist who is to start as a new student at the monastery school. His dark charisma and heretical ideas immediately cast a spell over April. When April begins to dream of witch burnings and churches full of blood, she begins to suspect evil, and together with her brother and her friend Ginger, sets off in search of answers which draw her deeper into the catacombs of the Golden City, and through the twists and turns of alchemy into irresistible orbit of Jack.