Sarah and her mother are Hersotes, people immortal and capable of magic. However, on a trip to an island as a young child, Sarah uses magic found in a Blood Moon to accidentally kill her mother who she thought could never die. Years later, Sarah learns of another impending Blood Moon, and the fears she has pushed aside resurface as she wonders what damage she might do this time. With the company of her close friends, Sarah journeys to that horrible island from her past in an attempt to discover the Blood Moon's dark secrets-secrets that could result in the deaths of not just one unfortunate...