List of Mako: Island of Secrets episodes

With Evie having a hard time adapting to her new life as a mermaid, Mimmi decides to use a shapeshifting spell from within Rita's grotto to turn Evie back to normal. The spell, however, doesn't work and, as a result, Evie is covered in a pink slime which keeps her stuck in her mermaid form. Zac hides Evie in the café's refrigeration room and then runs off to stop the spellcasting while Cam and Sirena keep Carly and the new waiter, Erik, from entering the room and seeing Evie with a tail.

With the full moon approaching, the mermaids plan to take Evie into the Moon Pool that night and teach her to channel the moon's influence, so she doesn't lose control again. Mimmi talks to Rita about the visions she's been sharing with Zac and thinks it is an ability she inherited from her mother, Nerissa, but Rita has no answers for her. Meanwhile, Cam convinces Zac to work together with Erik to unlock the merman chamber's secrets. To prevent interference from the mermaids, they have Cam cover for them. However, the girls see through Cam's deception and realise what Zac and Erik are up to. Sirena and Evie head to the Moon Pool while Ondina and Mimmi prepare to go stop Zac. They and Rita are approached by Veridia, the head of the mermaid council. She is determined to stop Zac at all costs and has them lead her to the merman chamber. Rita, worried that Veridia might harm Zac, follows them. The group confronts Zac and Erik in the chamber. As Veridia prepares to attack Zac, Rita intervenes, revealing that Zac's true mother is Nerissa and that he had always been a merman. Upon hearing this, Mimmi steps in front of Veridia, refusing to let her hurt her newfound brother. Ondina chooses to side with her best friend against Veridia. An angry Veridia brands Mimmi and Ondina as traitors and banishes them from the pod. Meanwhile, in the Moon Pool, Sirena successfully teaches Evie to control the moon's influence. Back at Rita's grotto, the news of Zac's true identity proves too much for him to bear. Feeling utterly overwhelmed, Zac goes home and talks to his parents, who appear to break down and tearfully tell him the truth.

The next full moon is approaching and Zac will have an opportunity to learn about what the merman chamber does. Ondina is worried about what might happen if Zac activates it but Mimmi refuses to go against her brother's wishes and intends to let him activate the chamber. At the Moon Pool, Ondina runs into Veridia who has come up with a plan to destroy the chamber by having Ondina use her power to turn the chamber's power against itself when Zac activates it. Ondina agrees under the condition that she, Mimmi, and Sirena be accepted back into the pod and Veridia agrees. Later, however, Zac changes his mind about activating the chamber when Rita informs him that he and Mimmi are descended from the merman who built the chamber and refused to activate it after falling in love with a mermaid. Ondina meets with Zac and manipulates him into continuing with his original plan to learn the chamber's purpose. Zac agrees under the condition that he goes alone. That night, Zac sneaks away to the merman chamber with Ondina following him. When Mimmi learns that Zac had lied through a vision, she and the others rushes to the chamber. When Zac enters the code into the chamber, it seemingly recreates the trident. As Zac reaches for it, Ondina stops him and prepares to carry out Veridia's orders. The others intervene, warning Ondina that destroying the chamber may destroy the island itself. Zac reaches for the trident again but it turns out to be a hologram that signifies the trident is necessary to start the chamber. With the trident already destroyed, the chamber's threat is seemingly over. The next day, Veridia lifts the girl's banishment and informs them that the pod will return by the next full moon.

Erik learns from Cam that while the trident was broken, the trident's stone that powers it wasn't. Erik concludes that it is the stone rather than the trident that can activate the merman chamber. Sirena reveals to Zac, Ondina, and Mimmi that she has kept the stone hidden at Rita's grotto the entire time. Although the stone has seemingly lost its power, it becomes active again when Zac touches it due to his stronger connection to Mako Island. Rita realises that the chamber's purpose is to drain the magic from the moon pool and all mermaids by amplifying the effect of the stone. Zac takes the stone and goes to hide it in a safe place. When Erik realizes Zac has the stone, he confronts him over. Erik believes there has to be more to the chamber's purpose besides destroying mermaids and becomes angry when Zac refuses to activate the chamber. He demands custody of the stone but Zac refuses to hand it over. Realizing the stone is not safe with him, Zac turns to Cam and asks him to hide it. Erik tries to bribe Cam into giving him the stone but Cam refuses to lose his friendship with Zac twice and, instead, gives it back to the mermaids. Erik later finds the stone in Rita's grotto and is confronted by Mimmi and Zac. Erik uses the stone to drain Zac's powers. With the stone now in his possession and Zac's powers inside it, Erik will be able to activate the chamber.

With the full moon approaching, Ondina tries to warn Erik not to activate the merman chamber, but Erik refuses to listen even to her. A now powerless Zac has seemingly given up despite encouragement from Mimmi, Evie, and Cam. Zac later musters up the courage and follows Erik to the chamber to try and stop him. The girls also race to the chamber to stop Erik. Zac fights with Erik for the stone but he shakes him off and finally activates the chamber. The girls attempt to destroy the stone with their moon rings, but it merely absorbs their power. The chamber drains the magic from the moon pool and slowly begins to kill the mermaids except Evie. Horrified by what he's done, Erik tries to deactivate the chamber but is unsuccessful. Evie arrives and helps an injured Zac to his feet. He successfully deactivates the chamber and saves the mermaids but seemingly dies in the process. Desperate to save her brother, Mimmi grabs the stone and places it over Zac's heart. The stone restores Zac's power and revives him. The stone then crumbles, ending the chamber's threat to mermaids for good. The next day, Ondina breaks up with Erik and he leaves the Gold Coast. Sirena reveals she's a mermaid to David. Veridia meets the group at Rita's grotto and praises Zac for his heroic actions. She makes him and Evie honorary members of the pod and gives Evie her own moon ring. The group joyfully swims out to greet the pod as they return to Mako at last.

As the mermaids prepare for their next encounter with the dragon, Weilan demonstrates a powerful Eastern mermaid spell called "Turn the Tide" which reflects any magic aimed at the spell-caster back to where it came from. Zac and Ondina are both determined to learn it and struggle in their efforts. Meanwhile, Mimmi volunteers herself and Ondina to cover for David while he works on a group science project. The two run into trouble when Joe shows up in the middle of Ondina's efforts to figure out Weilan's complicated spell on her own.

On the night of the full moon, the pod is determined to defeat the water dragon. Veridia, however, tasks Ondina and Mimmi with watching over the younger mermaids instead of fighting with the pod. Unhappy with being left out of the action, the two decides to disobey Veridia's orders and join the fight. Meanwhile, Zac and Weilan prepare to carry out their plan to have Zac lure the dragon into the Moon Pool before using "Turn the Tide" to counter it's fire breath. To get the pod out of the way, Weilan lies to Veridia, claiming the best course of action is to hide on the west side of Mako to catch the dragon off guard when it will actually appear in the east where the moon rises. Knowing Evie will try to stop him if she finds out what he's up to, Zac enlists Cam to keep her occupied until he returns. Unfortunately, Evie decides to join the pod in the fight and she enlists Carly to perform the same task as Cam. Later, Evie notices Zac and Weilan together and realises they are up to something. When Weilan finally tells Evie about their plan, she frantically swims off to the Moon Pool after Zac. The dragon soon appears and chases Zac into the Moon Pool where he finds Evie. Meanwhile, Mimmi finds out in horror what Zac is doing when she has a vision and Ondina realizes that Weilan had deceived them. Alone, Zac and Evie face off against the dragon. In the end, Zac fails to destroy the dragon and Evie is struck by the dragon's fire breath, causing her to lose both her tail and her powers. Instead of finishing Zac off, the dragon merely sniffs him and then leaves. Afterwards, Ondina furiously berates Weilan for lying to the pod and causing Evie to lose her tail and she runs off in utter shame. Heartbroken over the loss of her tail, Evie goes home after declining Zac's offer to walk her.

Zac finds a seemingly ordinary but beautiful seashell while swimming out on the reef. Later, when the mermaids visit Zac and see a picture of him from when he was younger, a nostalgic Zac casually wishes that they could have seen him from those days. The seashell suddenly sends the girls five years back in time where Zac is younger. When young Zac asks who they were, Weilan tells him that they're aliens. Confused, the girls leave and meet a younger Rita who does not recognize them. After realising that it was the shell that sent them to the past, they return to Zac's place to search for it. Meanwhile, in the present, Zac finds himself in an alternate world where Cam and Evie are a couple, Rita has moved away, and everyone believes him to be an alien obsessed nerd. Back in the past, the girls manage to find the shell, but young Zac begs them not to leave and an impatient Ondina hurts his feelings. The girls talk to young Rita again and convince her that they're from the future and she tells them how the shell works. Rita reveals that the shell is a wishing shell and only the person who found it can use it. The girls find young Zac at a birthday party for young Evie and ask him for his help after Ondina apologizes for being mean to him. When young Zac begs them to prove to the other guests that they're aliens, they feign ignorance and young Zac is humiliated. Mimmi apologizes to young Zac for this and saves young Zac's reputation with a brief magic show with her powers. Young Zac then uses the shell to send the girls back home and restore the present to the way it was.

Ondina and Weilan takes a class of young mermaid onto Mako Island to teach them how to walk on two legs. One of the mermaids named Amaris quickly gets the hang of walking and wanders off on her own to explore the island, forcing Ondina to go search for her. To make matters worse, Chris and Karl are sent to observe some sea turtles on Mako Island, right where Ondina and Weilan are teaching their class. Mimmi heads to the island to warn them of Chris and Karl's impending arrival and Weilan sends the other young mermaids to safety. Amaris soon runs into Chris and Karl and runs away frightened. As Chris, Karl, and the mermaids search for her together, Amaris continues to hide, fearful of interacting with land people. She then falls into the land entrance to the Moon Pool and is able to swim back to the beach where Ondina finally finds her. Amaris then apologizes for worrying everyone and promises to never wonder off on her own again. Meanwhile, Cam suggests modifying the recipe of the cafe's most popular burger to save money but David is against the idea. To resolve the matter, they ask Zac to act as their taste tester for the burgers. Ultimately Zac declares that the burger should be left alone.

When Chris finally asks Mimmi out on a date, she happily accepts. Although Weilan is delighted for her, Ondina is completely against the idea. As Mimmi enjoys a day at the beach with Chris, Ondina follows them in an attempt to protect her despite Weilan's insistence to back off. As Mimmi and Chris are about to kiss, Ondina creates a rainstorm forcing Mimmi to flee. Later, Ondina admits to Weilan that she ruined Mimmi's date because her own previous relationship with Erik ended in heartbreak and she does not want to see Mimmi suffer the same way. After comforting her, Weilan convinces Ondina that Mimmi needs to be free to make her own decisions. Although Ondina admits what she did and apologizes, Mimmi decides to not pursue a relationship with Chris out of guilt for lying to him. Meanwhile, Cam attempts to change the image of the cafe in order to attract more sophisticated and wealthier customers despite hesitance from Evie, David, and Carly. As they try to arrange a formal party, no one shows up much to Cam's disappointment. Carly convinces Cam that the cafe is fine the way it is and they draw in a crowd after making the party more laid-back. Weilan and Ondina get Chris and Mimmi to come to the party in an attempt to bring them back together. After steering away from the party to talk, Chris and Mimmi admit their true feelings for each other and finally become a couple after sharing a kiss.

Mimmi and Zac receive a vision of a mermaid whom Mimmi believes is their long-lost mother, Nerissa. Stunned to learn that Zac and Mimmi are Nerissa's children, Weilan reveals that she disappeared after facing a rebel mermaid named Aurora who threatened the Northern and Eastern pod. Zac and the other mermaids are hesitant to believe that Nerissa is still alive, much to Mimmi's frustration. Later, while watching Chris' football game with Ondina, Weilan, and Zac, Mimmi's moon ring glows and she is convinced that Nerissa is trying to reach out to her. Mimmi leaves the game to contact Nerissa, despite Zac urging her to let Nerissa go. Out at sea, Mimmi uses her moon ring in an attempt to reach Nerissa. To Mimmi's horror, the use of the moon ring summons the water dragon, which chases her into the canal. But instead of taking Mimmi's tail, the dragon spares her like it did to Zac before. Afterwards, Mimmi decides with a heavy heart that she must let Nerissa go for both her and Zac's sake. To give themselves some closure, Zac and Mimmi hold a memorial service in Nerissa's honour. Meanwhile, Cam's roles as both boyfriend and boss to Carly becomes frustrating and confusing to her. They attempt to find a balance with a system regarding two caps, but this proves ineffective. Cam eventually decides he would rather just be Carly's boyfriend and quits being the co-owner of the cafe. Later, Mimmi apologizes to Chris for bailing on him, but he starts to have some doubts about their relationship.

As Ondina continues to teach her mermaid class, she grows frustrated by her students' lack of interest. To liven the class up, Mimmi suggests showing them a spell that accelerates the growth of any living thing. Later, Weilan mistakes the growth spell ingredients for tea and offers some to Rita as she prepares for a job review to keep her position as principal, causing her to rapidly age into an old lady. After Rita tells them the ingredients for a reversal spell, Weilan and Ondina go to gather them while Mimmi keeps an eye on Rita. Rita reflects on her past and realizes that, although she had a fulfilling life on land, she misses her old life in the sea. Rita then realizes that she forgot one final ingredient for the reversal spell but has trouble remembering what it is. Meanwhile, the school board begins interviewing the science teacher for the principal job. Zac and Evie distracts the school board to buy Rita more time. Rita eventually remembers the final ingredient and the girls are able to complete the reversal spell to restore Rita to her normal age. Although Rita makes it to her review, she realizes how much she misses the sea and, to everyone's astonishment, quits her job as principal. Later, Veridia offers Rita a job in mermaid school and Rita takes Ondina's place as the teacher of the mermaid class.

The mermaids, along with Karl and Chris, attend a book signing at an exhibition for Secrets of the Deep, whose author had gathered lots of artefacts from incredible depths of the ocean. The author of the book turns out to be Rikki Chadwick from H₂O: Just Add Water. A mysterious bracelet at the exhibition is noted to be associated with the Jiao Long Dragon. The mermaids go to Shen's antique store where Weilan examines the painting of The Legend of Jiao Long. The painting reveals a mermaid using the same bracelet from the exhibition on the dragon in the legend. The girls suspect that Rikki is a mermaid, whose recovered bracelet can defeat the water dragon. The girls inform her of their real identities and of the dragon, but Rikki turns the girls away, unwilling to give up the priceless artefact she struggled so hard to obtain. Meanwhile, Chris becomes suspicious of Mimmi's behavior and begins to doubt that Mimmi really likes him. In an attempt to get some answers, Chris talks to Zac who insists that Mimmi has nothing to hide and that she really likes him but Chris is left unsatisfied. Later, the mermaids enlist Zac to help them steal the bracelet. The heist ultimately fails and the girls are forced to retreat when the police arrive. Afterwards, Chris confronts Mimmi on her secrecy but when she refuses to tell him the truth, Chris breaks up with her.

With the next full moon approaching, the mermaid council plan to unleash the full power of the Moon Pool to defeat the water dragon. When a clearer vision of Nerissa reaches out to Zac and Mimmi, they conclude that her spirit is trapped as the water dragon. Weilan learns from Uncle Shen that the bracelet actually broke the spell of a male human who was spelled as the legendary Jiao Long Dragon. Despite their pleas to use the bracelet instead of launching the power of the moon pool, Veridia denies Zac and Mimmi's request in fear of the pod being harmed. Meanwhile, Ondina and Weilan bond with Rikki as she shares her history with her and her friends becoming mermaids, eventually convincing Rikki to help steal the bracelet before it gets donated. With the bracelet on hand, Ondina and Weilan attempt to stop the council from using the Moon Pool while Mimmi and Zac confront the dragon, eventually restoring Nerissa to her true form. At the grotto, Nerissa reveals that an Eastern mermaid spelled her into becoming the dragon, unleashing a devastating attack on the Eastern pod, and then left into a deep sleep until Mimmi and Zac reunited. In the end, Zac contemplates informing his parents about his true origins, Mimmi reveals she's a mermaid to Chris and they get back together, Weilan is given a moon ring and intends to return to Shanghai to restart the Eastern pod with Ondina offering to join her and the girls invite Rikki to their pod (along with her friends).