A camping trip to mysterious Mako Island turns out to be much more than that for outdoorsy teen Zac. Unknown to him, the island is actually the domain of a pod of mermaids, three of whom -- Sirena, Nixie and Lyla -- should be guarding the Moon Pool. But they neglect their duties, and Zac falls in. The waters of the pool endow Zac with special powers, allowing him to transform into a merman when he comes into contact with water and forcing the mermaid pod to leave the waters around the island. Not all of them leave, however; the three transgressors are cast out of the pod and left behind. To rejoin their community, the girls must somehow travel on land and retrieve Zac's new powers. If they fail, they'll remain outcasts forever. Zac enjoys his newfound abilities, and the girls are sympathetic. What's a mermaid to do?