Plot

Their mermaid identities no longer a secret, Cleo, Emma and Rikki must evade a trap being laid by the devious Dr. Denman.

While Dr. Denman holds Lewis prisoner on her boat, she and Harrison trap the girls in the Moon Pool. Zane must choose between his father and helping the girls. Their only chance to avoid exposure is to give up their powers. Will they do it?—grrlpunk

The hunt for the now-identified mermaids intensifies as Dr Denman sets a trap for the girls at Mako Island forcing Zane to make a decision about where his loyalties lie. A lunar eclipse gives the girls an opportunity to free themselves from further pursuit by sacrificing their powers.

Now that the mermaids have been identified, Dr. Denman continues her pursuit of them by holding Lewis hostage on her boat and using his mobile phone to lure the girls to the Moon Pool, where she traps them. After discovering that the three mermaids are in fact Rikki and her friends, Zane is left torn about where his loyalties lie; with his father, or with Rikki. Eventually, his conscience leads him to set Lewis and the girls free (much to his father and Dr. Denman's annoyance), but the mermaids are not out of trouble yet. Knowing that Dr. Denman and the scientists will still come after them, the girls must make a tough decision. Miss Chatham tells them of the forthcoming lunar eclipse, and says that, if they enter the Moon Pool when the eclipse passes over it, it will draw their powers away from them. As normal girls, the three of them would be of no interest to the scientists, and would be out of danger. The girls make the choice to enter the pool, and while their powers seem to vanish completely, the next morning they find they've become mermaids again: the eclipse only affected them for 12 hours.

After Dr. Denman and Dr. Bennett have discovered that the three girls are mermaids, the girls are trying everything to prevent their exposure. However, they are caught and Zane finds out when his father brings him to the merpool in Mako Island. A hasty rescue is made, and the girls have to give up their powers during the lunar eclipse, so as to avoid being exposed to the world as mermaids.

After Dr. Denman and Dr. Bennett have discovered that the three girls are mermaids, the girls are trying everything to prevent their exposure. However, they are caught and Zane finds out when his father brings him to the merpool in Mako Island. A hasty rescue is made, and the girls have to give up their powers during the lunar eclipse, so as to avoid being exposed to the world as mermaids.