Piggley’s father tells him an old Irish tale about fairies disguising themselves as bugs and playing tricks on anyone who harms them. Soon Piggley and Dannan are convinced that fairies have turned Ferny into a flying beetle after he inadvertently smacks a bug on his arm. While Piggley investigates and experiments with ways to keep Ferny safe, Dannan hits the books to try and find a cure - and Ferny learns how much his friends care about him.