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.

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.