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.

Sophie uses Bella's idea for a fundraising concert and presents it as her own to Rikki to gain publicity for the cafe. Cleo's caught in the crossfire with Kim when Samantha moves in and puts her stamp on the Sertori home.

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.

Cleo's 16th birthday is approaching and she thinks that her father is going to throw another embarrasing birthday party. Meanwhile, Zane tries to find the 'sea monster' that he saw when he almost drowned.

Cleo and Kim are stuck with their cousin Angela who wants to go body boarding and causes a bird brained distraction when Cleo refuses.

Emma decides that she is not going to have her annual sleepover party due to what has happened to them. But Rikki and Cleo try to convince her otherwise. Meanwhile, Lewis conducts experiments on the girls.

Rikki is offered a job to collect rare fish. At first it seems perfectly fine, until she finds out the person that hired her is selling the fish for large profits.

Cleo decides to restart her friendship with Lewis and embrace her abilities, while Emma is shocked with the new supervisor who has big changes planned.

Rikki fears Ryan's explorations on Mako Island will uncover their secrets but Cleo and Bella discount her concern. She almost goes too far trying to stop Ryan from discovering the crystals in the Moon Pool.

Don gets a second job at the Marine Park on the Pirate ship and outshines Cleo, threatening the future of her Dolphin show. Bella and Will find difficulty trying to connect with each others' interests.

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.

Cleo's sister Kim finds her diary and thinks that Cleo and her friends are 'evil mermaids' and she plans to tell everyone. Meanwhile, Lewis goes to Mako Island to find out more about what happened to the girls.

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

Lewis is offered a great job with a marine biologist, but the girls are concerned that his interest will cause him to reveal too much information

The girls have problems with their new powers and Cleo finds that Lewis isn't helping. A new girl called Charlotte arrives and develops a crush on a certain charecter

Cleo is worried when she sees her dad around with another woman. When she arrives at their house, she turns out to be Charlotte's mother! Meanwhile, Rikki and Emma attempt to save the Sertori's dinner with their powers.

Emma has to take Eliot for horse riding lessons and the competitive perfectionist tries to be better than the instructor. Meanwhile, Lewis double dates with Charlotte and Cleo.

The girls decide that they should accept Charlotte, and the four work together when they need to join the volleyball team to avoid failing Physical Education.

With Will finding out about Mako Island, Bella tries to misdirect his search so that he will not discover the Moon Pool. However, Lewis and the girls find out that the Moon Pool is different.

At the marine park, Cleo seeks a job as a dolphin trainer. Meanwhile, until she and Bella reach an understanding, Rikki fires Nate's band, preventing them from playing in the cafe.

Cleo has to put off Lewis' romance plans in order to help Kim with her crazy love life. Meanwhile, Don meets up with a National Parks Manager, Samantha, and the two decide to date.

To get more interest in the cafe, Zane develops a dirt bike race. However, Rikki finds out that it is a scam. She and Bella decide to team up to teach him a lesson. Meanwhile, Lewis and Cleo find out something interesting about mixing the waters in the Moon Pool

Cleo's family and Sam go on a picnic to the beach, which leads to tension when Cleo refuses to go near the water. Kim abuses the fact that her father is happy in order to get lots of gifts. Will's sister Sophie competes with Bella to get the job Bella wanted at Rikki's Cafe.

Cleo's introduced to Ryan, a young geophysicist who's working for Samantha. Rikki doesn't react well to Cleo consulting Ryan about the Mako rock and a fracture begins to appear in the trio.

With Cleo's parents now divorced, Cleo is ordered by her dad to take more care of Kim, starting with taking her to a concert. But on the night, Cleo, Rikki and Emma all accidentally see the full moon, and take off to Mako Island, with Lewis in hot pursuit. Once there, the girls undergo another magical transformation in the Moon Pool, as a rare planetary alignment intensifies the power of the full moon – Emma's power is enhanced so that she can produce snow and frost, Rikki can conjure lightning, and Cleo can now control wind as well as water. After the moonstruck girls nearly harm Lewis, they realise that they must work to control their new powers, before anyone else gets hurt.