Cleo is trying to live a normal live, and one way of doing that is by getting a job at the Marine Park, all the while knowing that one splash of water could turn her into a mermaid. Despite Emma and Rikki's concerns about her new job, Cleo manages to keep her secret safe. But when Emma throws a sleepover party and someone spills a drink, things get a little tricky. Can the three friends still keep their fishy secret from the others, or will all be revealed?