A unusual and rare planetary alingment is set to cause the full moon to remove a mermaids powers if they enter the moon pool! Charlotte shows immunity and tries to reveal the girls secret before Lewis takes her to Mako Island. The girls follow and a battle erupts. But who will win?

Angry over the short friendship with the girls, Charlotte forces Lewis to choose between her and his friends. This results in Cleo to feel isolated and she runs away and gets lost. When he is informed, Lewis must make up his mind: Cleo or Charlotte?

Dr. Denman sets up a trap for the girls at Mako Island and Zane is forced to decide who he should be helping.

Zane is curious by Rikki's reluctancy to reveal where she lives. So one day, he eventually convinces her to reveal her home: a trailer park with her grouchy father.

Lewis is trying to find more information on the moon pool and stumbles across research on it by Max Hamilton from fifty years ago. Will Lewis reveal the girls secret to him in order to complete the puzzle?

In need of cash, Rikki decides to go and searching for a lost statue with a huge reward. But she lies to Emma and Cleo, which causes danger when Rikki is knocked out!

Zane's quest to find the 'sea monster' has led him to Mako Island. Rikki loses control of her powers as a result of the full moon and Zane finds her.

It's full moon and the girls insist that they don't need Lewis to assit his help as all three girls are staying at Emma's and Ash is coming over. When Cleo and Rikki fall under the moon spell, can Lewis stop them from revealing their secret to Ash?

Emma and Cleo are concerned about Rikki going out with Zane. They force Rikki to decide to either be with Zane or with them.

Rikki finds a locket that looks the same as Miss Chatham's in a Jewellery shop and she is determined to get it.

It's time for Emma's family's annual vacation trip, but she can't go as the risks are too high. But all her excuses don't go very well with her family. Meanwhile, with the return of Dr. Denman, Zane is closer than ever to cracking the girl's secret.

More friction arises, this time over Lewis' birthday party. Charlotte takes control and drives Rikki away from the party. However, things go out of hand and it is up to her to save the day.

Emma decides to change her look by colouring her hair red. Though nothing is that simple when you're half-mermaid. Zane asks Rikki out on a date.

With the school dance coming up, Emma and Cleo hope Byron and Lewis will ask them out. Meanwhile, Miss Chatham and Lewis are arguing about which is more important, magic and science.

On the night of a full moon, Lewis, Emma, Rikki and Charlotte accompany Cleo's family for a camping trip at Mako. When all three girls are affected by the moon, they are unable to stop the curious Charlotte...

Charlotte demands answers to why Lewis is hanging out with the girls so much. She starts to believe an excuse from Cleo, but then a discovery from inside Max's research brings her to the secret! Meanwhile, Ash decides to help Emma with her "fear of water"

Charlotte's stubborn nature and thirst for knowledge leads her to Max, who confirms her suspicions and leads her to the Moon Pool. Lewis meanwhile is having trouble trying to keep their relationship together.

The girls have to fake sick as a result of a thunderstorm, so their secret won't be discovered at school. But their 'sickness' attracts the attention of doctors.

Lewis enters the annual fishing derby. When Cleo sees him struggling, she decides to help him out with disastorous consequnces. Meanwhile, Rikki and Zane are trapped on a hotel balcony.

Lewis is puzzled when he dreams about Cleo being photographed by people. Later, he and Cleo take Eliot and Kim to the marine park. Meanwhile, Emma thinks something is up between Ash and Rikki.

Rumour has it that Cleo has a boyfriend and her friends and family are trying to find out who he is. Meanwhile, Zane continues his search for the 'sea monster' he saw.

Emma gets poisioned after cutting her finger on some coral and she begins to turn into a white scaled monster! Meanwhile Charlotte thinks Cleo is trying to break her and Lewis apart.

Zane learns of the myth of Ambergris, a fragrance that can make mermaids fall for any man that wears it. When he buys it, Nate ends up wearing it and Emma, Cleo and Rikki all fall for him!

For the first anniversary of the girls being mermaids, Cleo decides to throw a party. However, Emma and Rikki fall out following a fight between Ash and Zane and Cleo may have to celebrate alone.

Three very different teenage girls, Emma, Cleo and Rikki, facing everyday teenage problems. With a twist: they're mermaids; after discovering a magic place where they are given incredible powers over water that change their lives forever.