Off the coast of Florida, teenage mermaid Neryssa and her octopus pet Cara are enjoying a carefree life. But when Cara is snatched from their home and sent to the TideStar Marine Park in Miami, Neryssa has to trade in her tail for legs to stage a daring rescue. Posing as a human, Naryssa is forced to navigate the strange world of the drylanders, finding an unexpected ally in Lucas, a marine biology student, and the handsome Drake, who dreams of opening his own aqua park one day.