It's a full moon and the three mermaids Nixie, Lyla and Sirena are tasked to guard Mako and the moon pool. While Zac and Cam go camping on Mako island. When Zac falls into the moon pool they don't know what to do and leave him on the beach. The next day Zac finds out what he is and what he can do so he tells Cam. Because the girls let the "land boy" as they call him in the moon pool they are being cast out by their pod. So they decide to fix the problem.

Sirena, Lyla and Nixie must turn Zac back into a land boy. Using Sirena's Moon Ring, they give themselves legs and walk on land to begin their task.

In trying to get the Moon Ring back, the mermaids uncover Rita's secret.

Nixie and Sirena won't help Lyla try to "zap" Zac's powers, so Lyla decides to do it alone. This misfires when a waitress spills a drink on Lyla and Lyla rushes to hide in the refrigeration room before she transforms into a mermaid! When she can't dry her tail, Nixie and Sirena must save her before she is discovered!

Lyla and Sirena attempt to use the Moon Ring to stop the rain, but instead make it snow indoors.

Joe, David's brother has bought a new boat and decides to take it out for a spin. His fish finder locates a dolphin, but that dolphin is actually Nixie.

Zac's struggle with his merman secret intensifies when his girlfriend, Evie decides to throw him a pool party.

It's a full moon and the mermaids think that if they keep Zac out of the moonlight, he will lose his powers and return to his land-dwelling self. They stay with him in his garage on the full moon and attempt to keep him indoors.

While listening to Sirena sing, Lyla has an idea. If Sirena sings The Enchantment Song to Zac, he will fall under her spell. Everything goes south when David hears the song and falls in love with Nixie.

Against Nixie and Sirena's advice, Lyla goes with Zac to Mako Island. She steals Rita's Moon Ring to open the land entrance on Mako. But when the entrance suddenly closes, Zac and Lyla are trapped inside.

The girls fear their pod will never return. A despondent Nixie gives "advice" to a young boy named Ben. Zac researches tridents online and Cam snoops. Rita tells Lyla and Sirena about the trident and a pod of mermen that rose up eons ago.

Zac continues to try to find the trident. Lyla focuses on keeping him from it. Rita won't keep giving the girls money so Sirena makes bracelets for the Café to sell. While Sirena gathers shell for them, Zac catches a glimpse of her tail.

Rita and the girls worry about the upcoming full moon's effect on Zac. Nixie thinks they should let Zac find the trident so they can take it from him and hide it. Lyla thinks they should come clean with him so he'll in hopes that he'll understand and stay away from it. While Lyla warns Zac to keep away from Mako Island during the full moon, Evie sees them holding hands and breaks up with him. Cam discovers that the girls know Zac's secret but feels uneasy about them helping him. Under the light of the full moon, Zac goes after the trident with the girls close behind.

Zac starts to wonder why their principle, Rita, is helping Lyla, Nixie, and Sirena.

David and Sirena's relationship continues to grow, while Nixie and Lyla are worried she won't want to return to the sea.

Cam gets a new phone and films Zac swimming.

After finding a Moon Ring on the sea floor, Zac gives it to Evie. Now, the mermaids must get it back.

Zac is being watched by the mermaids, but with Cam's help he evades them.

After acquiring the Trident, Zac doesn't know how to turn it on.

Zac must find a place to hide the Trident from the Mermaids.

Aquata returns saying Sirena can come back to the pod, but Lyla and Nixie can't.

Rita's cat is turned into a human after walking through a bunch of mermaid powders.

Zac leads Lyla to the Trident; they fight for control of it and Lyla is knocked unconscious.

Lyla teaches Zac about mer history and the ocean but Nixie doesn't trust him.

Nixie agrees to help Cam unlock the Trident, but Evie wants to come along.

Cam betrays Nixie after planning to become a merman and rule Mako.

When the pod decides Zac is a threat and must give up his merman powers, two new mermaids, Mimmi and Ondina, are sent to make sure he obeys.

With Evie now a mermaid, Mimmi and Ondina try a dangerous spell to change her back to a human form, but the results are less than ideal.

When Zac has a powerful vision about his connection to Mako Island, he and the mermaids visit the island to investigate.

Erik's curiosity about the girls and Mako Island becomes a problem when he decides to investigate further.

When Evie's dad decides to take tourists on dive charters to Mako Island, the gang must find a way to change his mind.

Sirena gives Evie mermaid lessons, which rubs Ondina the wrong way, while Erik tries to get to the bottom of Zac and Cam's falling out.

With the full moon approaching, Zac's plan to avoid Mako Island is dealt a blow when his father insists they go on their annual camping trip.

When Mimmi goes to the first day of the new school year, things get out of hand fast when she runs afoul of the science teacher.

When a young mermaid follows Ondina back to Mako Island after a mermaid council meeting, it could spell trouble with the pod.

When David sees Evie in the water as a mermaid, it puts Zac and the girls' secret at risk unless they can convince David he's wrong.

Ondina adds too much jellyfish extract to Mimmi's body lotion, and the results put Principal Santos in dangerous waters at the marine park.

When Mimmi loses her moon ring in the Ocean Café's cooler room, it creates havoc for David and his brother's business.

On the night of the full moon, Zac and Erik swim to Mako Island and unlock the merman chamber, revealing a startling secret.

Zac struggles to come to terms with the news that he's a real merman, he's adopted and Mimmi is his sister.

After Cam absorbs moon pool water, he discovers he has power over water, which gets him a place in the trials for the school swim team.

Ondina sneaks Erik into the grotto to duplicate a pearl he gave her, but she accidentally turns him into a copy of Poseidon.

When Erik dives down and touches one of the rock outcrops on Mako reef, he's transported into a sphere of endless water with no way out.

When Sirena sees a video that shows a kayaker being lured by a mermaid's song, she starts to follow David obsessively, and he falls under her spell.

A surprise birthday party is in the works for Evie, who accidentally shrinks herself and falls into an aquarium after trying on Mimmi's mood ring.

Mimmi takes a job at the marine park, where she meets Chris, a young man who is desperate to get into a dolphin training program.

On the night of the full moon, Zac and Ondina sneak away to Mako, and Ondina reveals her plan to destroy the chamber.

Ondina doesn't want to choose between Erik and the pod when the pod returns. To cheer her up, Erik decides to throw a party in the café.

At the marine park, Ondina and Mimmi get into trouble when a dolphin splashes them and a little girl sees them transform into mermaids.

When Evie comes down with a fever that causes the temperature in the room to soar, Carly suspects that her friend is keeping a secret from her.

When Erik learns that the trident stone is the missing element needed to activate the merman chamber, Zac gives it to the mermaids for safekeeping.

The chamber's true purpose is revealed: to drain the magic from all mermaids. Zac risks his life to shut it down and restore the mermaids' magic.

Ondina is tasked with teaching the younger mermaids. A mermaid from China joins the pod. During a full moon ceremony, a terrifying beast emerges.

When marine park workers are sent to investigate the reported sea monster, the mermaids must create a credible explanation to stop further inquiries.

Weilan casts a knowledge transference spell on Zac to help him pass a biology test. But more than just science facts transfer from her body to his!

When Evie tries using her new moon ring to magically finish her chores, things quickly get out of control. Joe makes an upsetting announcement.

Weilan comes up with the idea of using a Chinese puzzle box to trap the sea dragon. Cam panics when Carly suggests they take dance lessons.

Evie's moon ring lesson with Ondina takes an unexpected turn. At the marine park, Mimmi discovers the reason for a rescued dolphin's distress.

Zac begs Weilan to teach him an Eastern spell few have mastered, which he hopes to use against the dragon. Joe encounters a water ball.

On the eve of the full moon, Ondina and Mimmi defy Veridia's orders. Evie becomes suspicious when she spots Zac and Weilan meeting in secret again.

After overhearing Ondina blaming her for Evie's loss, Weilan runs off. Meanwhile, Mimmi and Ondina combine their powers to try to restore Evie.

Zac realizes a shell he found has magical powers, and he accidentally sends the mermaids back in time five years, where they meet his younger self.

While Ondina teaches the little mermaids to walk on land, her fastest-learning student wanders off and soon runs into Chris and Karl on the beach.

When Mimmi and Chris go on a date at the beach, Ondina goes to great lengths to protect her. Cam tries to lure more upscale customers to the cafe.

Mimmi and Zac are startled by a mysterious yet strangely familiar vision. Cam's dual role as Carly's boss and boyfriend becomes difficult to manage.

Weilan mistakenly makes tea for Rita using a magic growth accelerator. Can the mermaids cure Rita before Mrs. Trumble takes over her principal job?

A priceless artifact recovered by a deep-sea treasure hunter provides a clue as to how the mermaids can defeat the water dragon.

The vision reappears to Mimi and Zac, this time speaking to them. Weilan learns a new detail about the dragon legend that suggests Nerissa is alive.