The Great Marsh is a magical place of spells, visions, and an ancient people. It is also a place of supernatural peril, and Circe Swinburne, the daughter of Puritans, is drawn to its shadowy mystery. From her birth, Circe has been haunted by pagan dreams and they intensify when fireflies begin to haunt her, flooding her with riddles. The tiny creatures guide her to a group living in secret, practicing the ancient ways of the Celts in the backwoods of the colony. She escapes to live in peace with them until one day a mysterious man appears with an unusual map. Circe is increasingly drawn to this dark and enigmatic Spaniard, and together they fight against the malicious Puritan witch hunters who are determined to execute her new family and destroy her way of life forever.