Serena Davidson leads two lives. At school, she's a morbidly obese, stupid, nerdy, bitchy, slutty, and a teacher's pet. But at home she's the scrawny vegetarian pushover. What would possess someone to wear a fat suit every day? And what happens when someone finds out?

Meet Marina Watson – she’s little, but no shrinking violet. She lives with her mum and step-dad, Rob. Life’s good, but there’s one thing she doesn’t get… Why she isn’t allowed to go in water?! For years, Marina’s mum has forbidden her daughter from having baths and swimming. She claims Marina has a terrible phobia of water, and will have an anxiety attack if she goes in it. But something doesn’t add up. Marina isn’t afraid: in fact, she’s never been more eager to dive into the deep end. One day, in a P.E. class, Marina finds herself doing just that - she accidentally falls into a swimming pool and transforms into a mermaid! Marina swims into the strange, exciting world of the ocean where she meets a whole range of interesting characters, and discovers some surprising truths along the way…