Born into a legacy of power and betrayal, Cassie is cast aside at six years old, condemned to a life in the crypts by her father, Daniel, to save his newborn daughter, Bella. This half-sister, the child of his mistress and true love, Marie, can only survive by living off, but never being close to, Cassie's energy. Isolated in the tombs, Cassie discovers through her mother's grimoire and her friend Jacob that she is the most powerful seer in her family's history since her ancestor Cassandra Bright. She also learns of a prophecy linking her to Asmodeus, the demon Prince of Hell, who once promised her ancestor a boon. On her deathbed, Cassandra uttered two final words: Help Cassie.