Caroline lives a life of luxury in the Fourth Terrace, made possible by her father’s prosperous shipping company. She daydreams about pirates, mermaids, and a life of freedom on the high seas, away from her overbearing mother and her high-society demands. Her daydreams seem to be at an end when her parents push her into an engagement with her father's handsome first mate, Bruce. But Caroline's father is not the gentleman he pretends to be. He is a pirate, and when Caroline is blamed for his crimes, she and her childhood friend, studious and timid Phineas, set off on an adventure of a lifetime.