Once every eighteen years, the isolated forest village of Weatherell is asked to send one girl to the god of the mountain to give a sacrifice before returning home. Twins Anya and Ilva Astraea are raised with this destiny in mind, and when their time comes, spirited Ilva volunteers to go. Her devoted sister Anya is left at home to pray for Ilva’s safe return. But Anya’s prayers are denied. With her sister dead, Anya volunteers to make a journey of her own to visit the god of the mountain. But unlike her sister, sacrifice is the furthest thing from Anya's mind. Anya has no intention of giving anything more to the god, or of letting any other girl do so ever again. Anya Astraea has not set out to placate a god. She's set out to kill one.