The powerful magician Prospera, formerly the Duchess of Vannes, has been shipwrecked for twelve years after her sister betrayed her. Her exile brings her to the Isles of Scilly, home to the Piskies, mischievous fairy-like creatures from Cornish folklore, led by Queen Joan the Wad. With a magical storm and a thirst for justice, Prospera sets her plan for vengeance in motion.