Emma, Rikki and Cleo are teenage girls with a secret – they’re still mermaids. They’re handling life pretty well but the threat of the full moon, and the strange effects it has on mermaids, looms. This time Lewis is certain he can help but things go awry and the girls are moonstruck. Under the influence of a full moon the girls’ powers are hugely enhanced and they wreak havoc on Lewis in his boat. The next day the girls have no memory of the night before as they each discover their powers are out of control. Lewis is missing and the girls are worried. They find him on Mako Island, fearful of them. They all realise things have drastically changed.