The trio investigate a sector called the Mystery Zone where several ships get wrecked on an island. They learn the evil witch Circe is responsible as she needs a young sorceress to overcome a curse in which she will turn to stone if she leaves the island. When Ariel arrives with Thundarr and Ookla, Circe gets her opportunity as she switches bodies with her and becomes a threat to the others as she tries to leave the island.