Even though she lives in a houseboat, Emily Windsnap doesn't know how to swim. Her mother has always cautioned her to stay out of the water. When swimming lessons start at school, Emily is excited to finally have the chance to learn. When she jumps in, she gets a strange, kind of scary sensation ... like her legs are stuck together. Emily later dives into the sea. She gets that weird feeling again, but this time she looks down to see that her legs are gone--replaced by a shiny, beautiful tail!