Cleo-Lewis Relationship

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Dating, In Love
First Met:
Not specified
First Kiss:
Started Dating:

Cleo Sertori and Lewis McCartney's relationship is one of the relationships in the H2O: Just Add Water series.

Season 1

Pool Party


Cleo wants to tell Lewis that she's a mermaid and wants to show him her powers with water. Emma and Rikki refuse to let her to tell that to him or anyone else about her powers and mermaidness. Lewis asks Cleo that she will go to Miriam's party. Cleo agrees, but changes her mind when she hears that it's a pool party. Cleo changes her mind every time and agrees to go. This makes Lewis to suspect that it's something wrong about Cleo. On the beach, Lewis tells Emma and Rikki, who are behind the rocks and are in mermaid form, that Cleo goes to the party and they tell him to go there to keep her out of trouble. At the party, Cleo pretends to have a cold, but Zane throws her to the pool just as Lewis arrives. Lewis finds out Cleo's secret and is shocked. Cleo begs Lewis for help and he helps her. Lewis promises to keep the girls' secret.

Catch of the Day


Lewis tells Cleo he thinks she's amazing, and Cleo snaps at him, thinking he was talking about her powers. After Cleo leaves, he replies "I didn't mean the powers", implying he may like her.

The Denman Affair

Denman's Laboratory

Lewis announces to the girls that a marine biologist, Dr. Denman, is coming and is planning to use her staff to discover the cause of the girls' transformation, worrying them because he will risk their secret. Following the first encounter with Dr. Denman, Cleo seems to be jealous when she sees that Lewis is so happy to see her. Cleo gives Lewis a sample of her DNA, but he accidentally leaves it behind when he gets caught by Dr. Denman. Dr. Denman discovers the sample and is shocked to see that it's mutating during the contact with water. Cleo discovers that Dr. Denman has created the article about the sample. Dr. Denman wants Lewis to be in her team and asks him to leave with her. Cleo becomes upset to find out that she will lose Lewis. Luckily for her and the other girls, Lewis didn't go, returns the sample and deletes the article.

The Siren Effect


Emma, Rikki and Lewis stay at Cleo's house to prepare for the full moon. Cleo is upset to see Lewis at her house because Don hates the boys. Cleo gets affected by the full moon and is transformed to a siren, causing her to sing very well. Lewis, along with the other boys, gets hypnotized by her voice. At her room, Cleo and Lewis kiss, but are caught by Emma, Rikki and Don and Lewis gets thrown out of the house by Don. At the end of the episode, after Cleo returned to normal, she tells Lewis that they're just friends. Don then interrupts their conversation and forces Cleo back inside and ordering Lewis to leave, much to the former's annoyance.



It's Cleo's 16th birthday and Don once again organizes a childish and embarrassing birthday party. Lewis is the only one who feels Cleo's suffering thanks to the parties. Cleo runs away from home and swims to Mako Island, but she's unaware that Zane goes there to find the "sea monster" he saw, with Lewis as a helper. Lewis notices Cleo's presence and manages to protect her secret. To cheer Cleo up, Lewis organizes the party at the cafe which makes her happy. Lewis gives Cleo a birthday gift and she kisses him on the cheek.



When everyone suspects Cleo has a secret boyfriend, Lewis is shown to be jealous. Before they think it is Zane, everyone thinks it is Lewis. At the end of the episode, Lewis tries to start a fight with Zane, as he thinks that Cleo and Zane are going out.

Hook, Line and Sinker


Cleo has always helped Lewis in the fishing competitions, but now she's a mermaid and has to be careful. Lewis tries to win a fishing competition, and when he is mocked, Cleo feels sorry for him and helps him to catch a fish. When Emma questions Cleo why she is helping him, Cleo is unable to answer. Then Emma says points out that they all know she likes Lewis. However, Lewis is accused of cheating and Don, who's the judge of the competition, kicks him out of the competition. Even worse, Don forbids Lewis to see Cleo anymore. Cleo blames herself for this and apologizes to Lewis. To cheer Lewis up, Cleo gets Emma's help in making the fishermen catch the fish with Lewis' new lure. It works as Don eventually starts to like Lewis, apologizing for his accusation and allowing him and Cleo to keep seeing each other.

Love Potion #9


Cleo wants Lewis to invite her for the school dance, but he gets too busy with trying to help the girls with their secret to make them waterproof to ask her. Fed up, Cleo gets herself invited by Nate. After Lewis introduces the waterproofing spray to the girls before the dance, he realizes that he forgot about the dance and apologizes to Cleo. Lewis invites her, but it's too late and she goes to the dance with Nate. After the girls escape to Mako Island due to their skin turning red because of the spray, Lewis realizes his mistake and apologizes. After Emma and Rikki leave to return to the dance, Cleo and Lewis reveal their feelings to each other and they kiss, becoming a couple.

Dr. Danger


Cleo and Lewis are swimming in the sea and swim to the moon pool. There, Lewis draws a heart on the sand and Cleo is very excited. Cleo and Lewis are making a picnic on the beach and are about to kiss, but are interrupted by Dr. Denman's return. Later in the episode, Lewis, distracted by his feelings for Cleo, draws the same heart on a flour on the cafe's table and ignores Emma's conversation about her troubles with her family until she tells him to concentrate.

Season 2



Because of her new and uncontrollable powers, Cleo accidentally sprays Charlotte. After the introduction, Lewis appears and Charlotte seems to have a crush on him. In help the girls to control their powers, Lewis gets too close to Cleo and does everything for her. This leads Cleo to break up with Lewis and become only friends.

The One That Got Away


Cleo sees Lewis with Charlotte and suspects that he will reveal the girls' secret to her. Cleo is determined to find out more about Charlotte, clearly growing jealous with how close she and Lewis are becoming. She finds Charlotte's diary and finds out that she loves RJ. Cleo demands Charlotte to tell Lewis about RJ. Charlotte tells Cleo that RJ is actually a novel, Romeo & Juliet, about which the play is prepared by the school. At the end of the episode, Lewis tells Cleo that Charlotte is just a friend and also asks if Cleo had changed her mind about their relationship. Cleo denies being jealous and claims that she wanted to know more about Charlotte for the sake of protecting the girls secret. Lewis is visibly hurt by this and leaves, leaving Cleo full of regret.

In Hot Water


Cleo gets fired from her job. Lewis' computer gets broken and unknowingly gets Cleo's job in need of money. Cleo gets angry at Lewis for "stealing" her job and this results in a war between them. Cleo refuses to accept Lewis' apology despite explaining he did not know he was taking her job. He grows angry at Cleo's unreasonable attitude and argues that the situation cannot be changed because Cleo got fired, which only infuriates her even more. Convinced that Cleo lost her job because of Lewis, Emma and Rikki make his job harder, but end up releasing Ronnie and putting Lewis the blame. Lewis bitterly informs Cleo that Emma and Rikki are the culprits responsible for releasing Ronnie, clearly angry at them for getting him into trouble. Cleo is equally angry at Emma and Rikki upon learning this. Cleo furiously confronts Emma and Rikki for their carelessness and yells at them for getting Lewis into trouble. The girls return Ronnie and Lewis convinces Mrs. Geddes to return Cleo's job for her. Cleo also forces Emma and Riki to agree to help cover the costs for Lewis' computer repairs to make up for all the trouble they caused him (though Rikki refuses to do this).

Missed the Boat


Cleo fails the biology exam because Lewis didn't help her in studying. After finding out that she can write the exam again, Cleo gets a new tutor, Charlotte, who gives Cleo a lot of homework. Charlotte is actually planning to get closer to Lewis who hoped to help Cleo. Charlotte asks Lewis to take her to Mako Island, so she can sketch it. After finding out that Charlotte buried her in homework to get closer to Lewis, Cleo, along with Emma and Rikki, follow Lewis and Charlotte to Mako Island. Cleo falls to the waterfall and Charlotte hears her. Lewis sees Cleo's tail and distracts Charlotte from seeing her by a kiss. After Cleo passes the exam, Lewis tries to tell Cleo that he just wanted to protect her secret, but she interrupts by telling him that there's nothing between them and he can do what he wants.

Get Off My Tail

Cleo Swimming With Lewis

Cleo is upset because Lewis is spending too much time with Charlotte and seems to miss him, but gets an advice from Rikki about that they can still be friends. After a failed attempt to ask Lewis for a juice, Cleo feels that he wants to be with just an ordinary girl until she gets a comfort from Rikki. Cleo takes Lewis for a swim in search for a new lure, resulting in him being 30 minutes late for his date with Charlotte. Near the end of the episode, Charlotte finds out that Lewis was with Cleo during his absence from the date and Lewis tells Charlotte that Cleo is just his best friend.

Double Trouble


Lewis has nightmares about Cleo being discovered as a mermaid. While chaperoning Kim and Elliot on their first and only date, Cleo jumps to the pool to save the big orange bear that Kim got from Elliot, but she threw it to the pool. The people see Cleo's tail, but they don't know what is this. Fearing that his nightmare is coming true, Lewis rescues Cleo and tells everyone that it was just a bear.

The Gracie Code, Part One


In an attempt to figure out more about the magic of Mako Island, Lewis finds the news about Max Hamilton who made research about the island. Max, however, rejects Lewis after the ask about Mako Island. Max changes his mind after seeing the locket on Cleo's neck. Max tells Lewis that he will give him his research if he'll get the locket. Cleo's locket gets broken and Lewis gives it to Max in order to fix it. Max convinces Lewis to take him to Mako Island. They arrive just as Cleo does it too. Max discovers Cleo's secret and tells her and Lewis that he created the lockets, knew the secret of Miss Chatham, Gracie and Julia, made research about the island, and that he was Gracie's boyfriend until she dumped him because of the research and the strain she felt from being caught in two worlds. Cleo tries to offer Max comfort when he blames the breakup on himself. She tells Max that people can do things without understanding why at the time and then realize too late that it was a mistake, a direct reference to how she broke up with Lewis and then regretted doing so for a long time. Max warns Lewis to stay close to Cleo and gives him the locket and research. Lewis later gives the locket to Cleo and tells her that they can see each other again soon.

And Then There Were Four


The girls ask Lewis to get rid of the research because Charlotte saw Gracie as a mermaid in a film. Lewis gives the research back to Max, but Charlotte has followed him and Max tells her the truth. Charlotte gets angry at Lewis for lying to her and runs away from him... right to Mako Island and discover the girls' secret. Cleo attempts to comfort Lewis after his fight with Charlotte and insist he should not be so hard on himself. Before Charlotte turns into a mermaid, Lewis tells Cleo that he liked to talk with her and misses it, while Cleo feels the same. The following day when Cleo asks Emma and Rikki how she should do her hair, Rikki is prompted to ask what took place between her and Lewis which suggests Cleo may have been interested in dating Lewis again if his relationship with Charlotte ended.

Sea Change


Charlotte tells Lewis to not talk with Emma, Rikki, and especially Cleo. Despite learning of Charlotte's venomous nature, Cleo considers giving her a second chance out of respect for Lewis, but Emma and Rikki refuse. She is even more upset when they say that Lewis is not their friend if he is with Charlotte, and refuse to listen to her. Cleo is unwilling to give up on Lewis and feels like she no longer has Emma and Rikki for support. Charlotte lies to Cleo that Lewis no longer wants to do anything for her and steals her locket, lying to Lewis that Cleo gave it to her on her own accord. Cleo is convinced that Lewis cares more for Charlotte than her. Cleo leaves a heartbroken message for Lewis, but Charlotte steals his phone. Cleo runs away from home, feeling isolated, lonely, and abandoned. A heart-broken Cleo swims to the Mako Island's shark area. Emma and Rikki are unable to find her. Lewis finds his phone in Charlotte's bag, hears Cleo's message and finds out that she's missing. Lewis gets a help from Max and is determined to find Cleo. After finding out that Charlotte was lying over the whole time, Lewis brutally breaks up with her. Lewis rescues Cleo and they get back together.



Cleo and Lewis have got back together and are caught kissing by Emma and Rikki before the full moon. After Charlotte attacks the girls, Lewis warns her about the full moon. Charlotte gets affected by the full moon and attacks Emma's house while Ash is there in hopes of explanation about Emma's secrets. Lewis asks Charlotte to go with him to Mako Island. Cleo follows them to find out along with Lewis that Charlotte is planning to make the girls lose their powers because in that night the planets will be in a line with the moon and a mermaid in the moon pool at the time will lose her powers forever. Emma and Rikki arrive and a 4-mermaid fight begins. Charlotte is defeated and loses her powers. Charlotte promises to keep the girls' secret and Lewis returns the locket to Cleo.

Season 3

Valentine's Day


It's Valentine's day, but Cleo is upset to know that Lewis wants to take her for a "fishing" date. Cleo gets fed up with this and leaves Lewis to help Kim get out of control love life. At the end of the episode, Lewis arrives in a tux and holds the rose in order to ask Cleo out and she accepts.

Big Ideas

Cleo Surprised

Cleo fears for the water tentacle's attack during the next full moon. Lewis is determined to find the tentacle, but Cleo wants to help him. Despite Lewis' protests, Cleo invites Will to her house to talk with him about the encounter with the tentacle. Lewis gets angry at Cleo for not listening to him and tells her that he wants to protect her, as he is her boyfriend. After a conversation with Will, Cleo and Lewis check the waters from the Moon Pool and the waterfall and mix them, resulting in them to turn to a water floating in mid-air.

Secrets & Lies

Cleo And Lewis Laughing

Lewis tests the moon pool water at school and gets caught Ms. Taylor. Ms. Taylor sees the water and mistakes it as a science project. Cleo gets angry at Lewis to find out that thanks to this the girls' secret will be in danger. Lewis is forced to present the water to the class, but Cleo helps him with her powers to create the duplicate water and later do an alternative project.

The Sorcerer's Apprentice


Lewis tells Cleo to remove the water and return it to the waterfall. Cleo ignores him and gets some of the water to experiment it with the girls' powers. To keep Lewis from finding out, Cleo sends him to go for golf with Don. At the end of the episode, Cleo admits to Lewis for ignoring him and promises to get rid of the water.

To Have and To Hold Back

Goodbye Kiss

Lewis gets an e-mail from American biology institute that he got in, but he has to start now and to leave quickly. Lewis tries to tell Cleo, but fails due to the announcement of Don and Sam's wedding. Instead, Lewis tells that to Rikki, who tells that to Bella. Following a discussion about Lewis' departure, Kim overhears it and tells Cleo that Lewis is leaving. Cleo gets upset and refuses to talk with him anymore. Before Kim ruins the wedding held in front of the cafe, Lewis tells Cleo that he's not going because he loves her. At the end of the episode, after the wedding is resumed at Mako Island, Cleo tells Lewis that she wants his dreams to come true and persuades him to go. After assuring each other that they will meet again one day, Cleo tearfully says goodbye to Lewis. Lewis leaves and Cleo says at least they'll be sharing the same emotion.


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During the graduation, Cleo is overjoyed to see that Lewis has come back. When Cleo asks him why he came all that way to see her, Lewis jokes that he heard "there's a new science genius in town" and he wanted to "check out the competition". Cleo is greatly amused by this and she and Lewis kiss tenderly. The newly reunited couple then dance to Bella's music as the show ends.