FBI Agent Ella Dark has studied serial killers from the time she could read, devastated by the murder of her own sister, and has gained an encyclopedic knowledge of murderers. But when victims of a new serial killer appear with a mysterious key left on each body, Ella knows she's up against a diabolical mastermind. What might each key unlock?FBI Agent Ella Dark, 29, is given her big chance to achieve her life's dream: to join the Behavioral Crimes Unit. Ella's hidden obsession of gaining an encyclopedic knowledge of serial killers has led to her being singled out for her brilliant mind, and invited to join the big leagues.In a wild game of cat and mouse, Ella must track these keys to their sources, and discover the twisted secrets hiding inside them.But when the keys strike too close to home, everything changes.