It's a full moon and the three mermaids Nixie, Lyla and Sirena are tasked to guard Mako and the moon pool. While Zac and Cam go camping on Mako island. When Zac falls into the moon pool they don't know what to do and leave him on the beach. The next day Zac finds out what he is and what he can do so he tells Cam. Because the girls let the "land boy" as they call him in the moon pool they are being cast out by their pod. So they decide to fix the problem.