It's nearly the end of the holidays and Cleo and Rikki are about to face their last year of high school without Emma, who has gone overseas with her family. Together with Lewis, they're confident they know everything there is to know about Mako Island, especially now that they no longer have to worry about the effect of the full moon. But when water attacks the girls on a full moon, they realize a new, potentially dangerous force is developing on the mysterious island, and a boy with freakish free-diving skills who stumbles upon the Moon Pool could hold the key to understanding the powerful energy... Thankfully they find an ally in Bella, a new girl in town who reveals an equally surprising twist: she too is a mermaid with extraordinary super powers. Together, the new trio face phenomenal challenges as they discover the dark secrets of Mako Island and realize their destiny as mermaids.
