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

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, 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.

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.

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.

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

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.

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.

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

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

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

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.

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

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

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

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

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.

Cam gets a new phone and films Zac swimming.

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

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.

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.

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.

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.

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.

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

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.

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

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

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.

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

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.

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

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 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.

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 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.

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.

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.

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