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

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

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.

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.

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.

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.

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.

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.