Fiona O'Malley has a secret: She was born with a fin on her back. Her parents are ashamed of this fact, and after they try unsuccessfully to have it removed, do everything they can to keep the fin a secret. But secrets have a way of getting out. When her classmates discover Fiona's secret, they make fun of her, and most of her so-called friends desert her. They make fun of her by calling her Fiona Finn. If it weren't for two friends who stand by her throughout the name-calling at school, she would be completely miserable. Only two people see the beauty in her unique difference. When danger strikes, Fiona is finally able to show the world that being different isn't a bad thing to be.