H2O: Just add Water

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.

Cleo uses her mermaid powers to avoid a sprinkler and inadvertently splashes Charlotte, the new girl at school. Lewis and Charlotte meet and it’s clear she likes him straight away. With the girls’ mermaid powers turned up to max, Lewis tries his best to help but his attempts only cause Cleo to feel crowded by him.

Zane’s back in town and still in love with Rikki. Although he believes she’s not a mermaid anymore, things are still tense between them. Rikki assures Emma she can handle Zane; they broke up and that’s all there is to it. As Zane continues to try to win Rikki’s affections, he realises she’s still a mermaid and saves her from the threat of discovery.

Rikki comes to stay at Emma’s house and stirs up the family unit by messing up the order of things. In trying to compete with Rikki, Emma tries to rebel and throws a party. Meanwhile Lewis wants to know why Cleo broke up with him; concerned that he’s not masculine enough for her.

Cleo notes that Don seems to be down since her mother left. Later, Lewis finds an old book on mermaids and tests out a potion recipe on the girls, supposed to grant wishes. Cleo instantly thinks it could help get Don and her Mum back together. They make the potion and it doesn’t seem to work.

Life isn't the same at Cleo's house since her mother left. When it appears that Don has a girlfriend - Cleo and Kim are horrified, thinking this means a step-mother. Meanwhile, Charlotte is making more moves on Lewis, making Cleo increasingly jealous. Don organises a dinner and Cleo is shocked to find her Dad's new partner is Charlotte's mother!

Cleo has been getting into some trouble with her boss Mrs Geddes at work and when Ronnie the dolphin splashes her, Cleo laughs and is fired. At the same time, Lewis finds himself in desperate need of a job after his laptop dies and, unbeknownst to ...

Riding their dirt bikes, Zane and Nate stop in a trailer park to look at a classic Harley. Nate steals a badge from the bike and Zane is busted by the owner - little does he know it's Rikki's dad. Later, embarrassed by her family's financial situation, Rikki hides where she really lives from Zane. Rikki has to overcome her shame about her background and introduce her dad to Zane.

Elliot is going to horse riding lessons and Emma is cornered into taking him. Emma meets Ash - a handsome horse riding instructor. They clash immediately. Emma tries to prove herself and goes too far. When a horse falls ill Emma must use her powers to fix the situation. Meanwhile, Lewis asks Cleo to accompany him to a formal awards night in a limo.

Cleo is failing at school. Lewis waits for Cleo to ask him for help, giving Charlotte an idea - she volunteers to help tutor Cleo! Cleo is horrified but is forced by Don to accept. Charlotte takes the opportunity to set Cleo mountains of homework ...

Zane hears of treasure under the ocean and enlists Rikki to help find it, after all a mermaid can search the bottom of the ocean pretty fast. Rikki is reluctant until she discovers her dad is having trouble paying the bills - and they might be forced to move. Rikki gets Emma and Cleo to help, but conceals her true reasons for wanting the treasure.

Emma starts acting very weird after pricking her finger on a mysterious barb of coral, suddenly becoming ravenous for things like anchovy flavoured fish food! Cleo's fish, Hector, exhibits the same behaviour. As Hector begins to look very sick, Emma turns into a mermaid at the marine park, swimming about in front of the glass in the viewing area.

Don forces the family to go camping on Mako Island during a Full Moon. Cleo can't get out of it so invites Emma and Rikki for back-up. Lewis inveigles himself to go too but when he tells Charlotte, she pressures him into taking her as well! The girls are furious with Lewis but he's in a bind.

Emma is annoyed to find the one guy she can’t stand suddenly appearing around the juice bar - Ash. When she thinks she’s going to get a promotion at work, Emma is even more annoyed to find that Ash has been given the job ahead of her. As Emma and Ash clash over how the juice bar is run, we discover it’s over a lot more; they’re secretly attracted to each other.

Nate is still trying his best to get Cleo to like him but to no avail. Lewis and Zane find an old myth about mermaids is true - the scent of ambergris sends them wild. Ambergris was once used in perfumes and is deposited by whales, it's extremely rare but Zane acquires some.

Lewis has a bad dream about Cleo being discovered as a mermaid. Elliot asks Lewis for advice on girls and Lewis obliges, just to keep him happy. Elliot asks Kim out on a date to the marine park but Kim goes along with it just to take advantage of Elliot paying for everything. When Don forces Cleo to go as chaperone and Elliot begs Lewis to come, Lewis and Cleo find themselves on the date too.

Ash keeps trying to ask Emma out but she won't hear of it - it's a full moon tonight. Cleo and Rikki goad Ash into being bold with Emma - but they don't count on him turning up at Emma's place in time for the full moon! Ash organises a romantic dinner just for him and Emma.

It's one year since the girls became mermaids and Cleo decides to organise a special party just for them but when Zane and Ash clash at the juice bar, Rikki and Emma take their boyfriend's side in the argument. Soon Emma and Rikki aren't talking to each other. No matter what Cleo tries, the friendship is still strained.

Lewis continues to search for clues to the magical effects of the moon pool. He discovers someone called Max Hamilton did research fifty years ago on the strange properties of Mako Island. Lewis tracks the old man down. Max is cagey and plays a cat and mouse game with Lewis. But it becomes clear the old guy knows a lot more about mermaids than Lewis first thought.

Lewis searches through a research folder on mermaids given to him by Max, somewhere in the research lies a clue to how all this happened. Charlotte becomes jealous of how much time Lewis is spending with his ex-girlfriend Cleo. When Charlotte visits Cleo, she sees a picture of Gracie on the wall and recognises her as her grandmother!

The girls want Lewis to destroy Max’s research folder; Charlotte is getting too close. Reluctant to give it up, Lewis decides to take it back where it belongs - to Max. Suspicious, Charlotte follows Lewis to Max Hamilton. Max tells all to Charlotte when he discovers she’s the granddaughter of his one true love - Gracie.

There's a fourth mermaid in town - Charlotte! Emma, Rikki and Cleo reluctantly have to deal with the newcomer. Charlotte is overjoyed, thinking this is the best thing that's ever happened to her. No matter how much they all try to explain how tricky it is being a mermaid, Charlotte won't listen.

Nate bullies Lewis, pretty much because he can, and when Nate's jet-ski is damaged he blames Lewis, demanding payment. Meanwhile Emma, Rikki and Cleo continue to have problems accommodating Charlotte as a mermaid, she won't listen to any advice. Charlotte takes their attempt to help as an attempt to boss her around.

It's Lewis's birthday. Cleo and the others have some ideas how to celebrate but Charlotte quickly takes over and organises a surprise party for Lewis. Charlotte's plans don't seem to be about Lewis and Rikki eventually has enough and leaves. The party is at Charlotte's house with all of Charlotte's friends.