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.

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.

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.

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.

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

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

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.

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

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.

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

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.

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.

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.

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.

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

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.