Annoying Miss Popularity, Miriam, is having a pool party that the girls don't want to miss. But it's a risky activity for three mermaids: their secret could be out. Spurned by Lewis, Rikki discovers her mermaid power is to boil water at will! For a hot-head like Rikki, this is dangerous. Meanwhile, Cleo's close friend Lewis is getting closer to finding out about the girls; almost busting Emma and Rikki, as mermaids. At the pool party, Cleo's plan not to go swimming goes out the window as Zane and his mates toss her into the pool. But luckily the guys walk away before she turns into a mermaid. The only thing is – she needs someone who's not a mermaid to get her out – Lewis.
It is a normal day in the Gold Coast, but Emma and Cleo are having mermaid troubles in their morning work. Meanwhile, Rikki is happily having a swim. The three girls meet up before school and have an arguement over whether or not to tell anyone.
At school, Miriam, a popular girl, is throwing a party for surfer Byron. The girls think of going until they discover it's a pool party. However, Emma thinks that if they find a form of control then they could still go, but Cleo refuses to swim. After a near encounter with Lewis, they go to Emma's and she and Cleo moan and anger Rikki, who stomps away.
At the JuiceNet, Cleo and Lewis are talking and Lewis ends up arguing with Zane until Byron stops it. Cleo then says she will go to the party. Emma is being questioned by her parents about swim training and she gets moody.
Pool Party is the next day. Lewis chats to Rikki, who discovers her power: heating water when she boils Lewis' drink. She then mets up with Emma and they go to the beach and Lewis comes down and says Cleo's at the party and the girls send him off.
Cleo is at the party, pretending to have a cold. But Zane and his friends get to her and throw her in the pool just as Lewis arrives. They all leave and Lewis discovers Cleo's secret. Emma and Rikki arrive and Emma freezes the door handle to the house. Lewis gets Cleo out of the pool and Rikki boils the water. They four leave and discuss the situation and Rikki threatens Lewis not to tell and they look out over the sea.