Book 4

A Sleepover Tail

by Nickelodeon

Published 6 July 2009
Cleo is trying to live a normal live, and one way of doing that is by getting a job at the Marine Park, all the while knowing that one splash of water could turn her into a mermaid. Despite Emma and Rikki's concerns about her new job, Cleo manages to keep her secret safe. But when Emma throws a sleepover party and someone spills a drink, things get a little tricky. Can the three friends still keep their fishy secret from the others, or will all be revealed?

Book 5

Sequins for Sea Queens

by Nickelodeon

Published 1 January 2010
The Marine Park is hosting the "Miss Sea Queen Beauty Pageant" and Cleo is planning the make the most spectacular costume the world has ever seen just so she can beat Miriam, who is desperate to win. Cleo is so distracted with putting her costume together that she doesn't realise that her little sister, Kim, has stolen her diary! When Kim reads the diary she's shocked to discover that Cleo and her friends are mermaids, and hatches a plan to expose them for what they really are in front of everyone! Can Cleo and the girls keep their secret safe?

Book 6

First Crush

by Nickelodeon

Published 29 April 2010
When Rikki agrees to look after Emma's younger brother, Elliot, she reluctantly takes him to the beach for his surfing practise. Rikki takes great care to stay on dry land whilst Elliot is in the water, after all, she wouldn't want to turn into a mermaid in front of a beach full of people! But when Elliot gets into trouble, Rikki has no choice but to jump in the sea and save him. Being rescued by Rikki has a strange effect on Elliot and he starts to develop a crush on her, which Rikki isn't exactly pleased about! Will Elliot be able to keep her secret?

Book 7

Moon Spell

by Nickelodeon

Published 5 August 2010
Emma has been busy organsing a surprise birthday party for her dad and when the evening finally arrives it looks like everything is going to plan. But when the clouds part to reveal a full moon something funny comes over Emma. Spellbound with full-moon madness, Emma begins to act very strangely, much to the dismay of the other party guests. Cleo, Rikki and Lewis must do their best to stop their friend from flirting with boys and guzzling down her weight in sardines! But more importantly, can they stop Emma from revealing to a room full of people that she's a mermaid?

Book 8

Testing Times

by Nickelodeon

Published 6 January 2011
When the world-famous marine biologist, Dr Denman, comes to town there is much excitement. For budding scientist, Lewis, it's a dream-come-true as he might be able to work as her assistant. He might also be able to learn more about why his three friends, Cleo, Rikki and Emma, turn into mermaids everytime they're splashed with water. But as Lewis spends more time at Dr Denman's lab, Cleo and her friends begin to worry that they secret could be under threat. Could they end up as lab rats?

Book 9

H2O: Hot Stuff

by Nickelodeon

Published 9 June 2011
Life as a teenager can be strange enough, but what if you grow a mermaid tail whenever you come into contact with water? Follow best friends Cleo, Rikki and Emma on more fun adventures as they try to keep their secret ~ that they turn into mermaids every time they're splashed with water ~ hidden from everyone else!

Book 10

H2O: In Too Deep

by Nickelodeon

Published 4 August 2011
The Juice-Net cafe is hosting a short film contest based around the theme of 'heroes', and everyone wants to enter. While Rikki and Cleo are roped in to doing a film about Emma's mum, Zane and Lewis hit the waters around Mako Island to film Zane windsurfing. Meanwhile, Rikki isn't convinced that Emma's film idea will win them the prize, so she sneaks off to make a film of her own, featuring some impressive underwater footage of sharks. But when Zane falls off his windsurfer, right in the middle of Mako Island's shark breeding ground, it's Rikki who finds herself being called a 'heroine' when she has to help rescue him!

Book 11

Mermaid Emotions

by Nickelodeon

Published 27 October 2011
As a former swimming champ, Emma appears to be the perfect person to coach Byron and help him to finally beat Zane in a swimming competition. And with Emma and Bryon spending so much time together training, it looks like a blossoming romance could be on the cards. But life as a teenage mermaid can be complicated and, knowing that she must keep her secret safe, Emma backs off before they get too close. Will their friendship end before it's even really begun?

Book 12

H2O: Siren Status

by Nickelodeon

Published 2 February 2012
Cleo's natural singing voice isn't the best...in fact, it's awful! But when the Full Moon appears, Cleo entrances Lewis, Byron, Zane and the other boys in the neighbourhood with her beautiful singing. In the midst of her new-found siren status, Cleo shares a special moment with Lewis. But when the moon sets, will they remember their kiss in the light of day?