Annoying Miss Popularity, Miriam, is having a pool party and the girls want to go. But being around water is risky, especially when Zane tosses Cleo into the pool. Lewis is the only one around to help so he finds out their secret.

Rikki, Emma and Cleo discover that sea turtles are being captured by fishing nets. When Rikki and Emma attempt to rescue the turtles by cutting the nets, it causes the fisherman to think that there is a rogue shark roaming their ocean.

Emma gets into trouble babysitting her little brother Elliot. She goes to Lewis for help when Elliot develops a crush on Rikki.

Miss Chatham gives Cleo a warning that she doesn't quite understand. Until Emma finds herself in a trance and unable to change back from a mermaid under a full moon.

Byron asks Emma for help with training the school's swimming team and Emma has some trouble deciding whether or not to help out in her current situation. Meanwhile, Lewis continues to experiment on the girls, which annoys Rikki.

The full moon gives Cleo a power to put guys in a 'trance' and she suddenly gets a rush of admirers.