Sirena, Lyla and Nixie are three young mermaids from the Mako Island pod. It is their sole duty to keep trespassers away from the magical Moon Pool, but on the night of a full moon, the mischievous mermaid girls neglect their duties. Zac, a land dweller, enters the Moon Pool and forms a special connection with Mako. He is given a fish-like tail and amazing powers. The mermaid pod is forced to leave Mako, leaving behind the three mermaid girls, who have been cast out of the pod. They know there's only one way they will be allowed to rejoin the pod: They must get legs, venture onto land and take back Zac's powers -or risk being outcasts forever.