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.

Cam gets a new phone and films Zac swimming.

Zac is being watched by the mermaids, but with Cam's help he evades them.

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.

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.

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.

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.

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 is tasked with teaching the younger mermaids. A mermaid from China joins the pod. During a full moon ceremony, a terrifying beast emerges.

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 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.

Evie's moon ring lesson with Ondina takes an unexpected turn. At the marine park, Mimmi discovers the reason for a rescued dolphin's distress.

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.

When marine park workers are sent to investigate the reported sea monster, the mermaids must create a credible explanation to stop further inquiries.

Weilan casts a knowledge transference spell on Zac to help him pass a biology test. But more than just science facts transfer from her body to his!

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

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.

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

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.

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.

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 begs Weilan to teach him an Eastern spell few have mastered, which he hopes to use against the dragon. Joe encounters a water ball.

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