A lovely wood nymph, bored with life and "tired of being a humdrum fairy year in and year out", begs to be transformed into a mortal for the space of one year, "to gain exciting experiences". So she becomes a young knight, Prince Marvel, and sets out to seek adventure. In his explorations of the island, the Prince comes to the court of King Terribus, who, because of his dreadful ugliness, is a cruel and terrible ruler. Prince Marvel has not lost his fairy powers, and he transforms the King's features until he is quite handsome, thus winning Terribus's gratitude and friendship.

A high-light of the story is the visit to the land of Twi, where everything is double and the singular kind of person that we consider quite complete is only half a man—and very singular indeed—to the inhabitants. Other adventures follow, and the Prince has had enough excitement to satisfy him when he must return to his original form at the end of the year.