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.

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

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.

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.

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.

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

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.

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

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

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

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.

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.

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.

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

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

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.

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.

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.

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.

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.

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.

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

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

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.

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.

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.

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

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

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

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.

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.

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

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.

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

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.

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!

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.

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.