When the US Marshals Serial Crimes Tracking Unit comes knocking at Aislinn Cain's door, she is given a chance to use her past to save other people's futures. She has survived attacks by two different serial killers and devoted her life to studying the darker side of human history. A new killer is using medieval torture methods to slay his victims. She can give them a glimpse into his twisted world, but not without a cost. If she opens herself, she risks falling into the depths of her own darkness. Can she afford to help, knowing that the cost could be her own humanity?