It was the afternoon of the full moon. Everyone was getting ready to go to the Merman Chamber on Mako Island. Will and Lewis were told that they should stay at Rita's, but Lewis was not pleased about this.

"Erik has taken my girlfriend!" Lewis yelled.

"And we'll get her back," Ondina promised. "But you and Will don't have magic. It will be dangerous enough for us."

Lyla and Evie were excused from the trip as well, as Rita said they needed recovery time.

"What about the full moon?" Emma asked. "Won't we go crazy?"

"You should get there long before the moon rises," Rita promised. "When you're in the Chamber, you shouldn't be affected.

Mimmi wanted to go with Zac to the Merman Chamber, but Zac wouldn't let her.

"I want to help!!" Mimmi said to Zac.

"I know, but I don't want you to get hurt," Zac said, putting his hands on her shoulders. "I can't let anything happen to you."

"And I don't want anything to happen to you either!" Mimmi cried. "Please Zac, Erik is so powerful, you'll need all the help you can get!"

"And I'll have Ondina, Emma and Nixie with me," Zac told Mimmi.

"Mimmi, you can stay here and help me prepare the blue coral to be added to the medicine for Rikki?" Rita suggested.

Mimmi glumly walked over to Rita to look at the blue coral. Zac, Ondina, Nixie and Emma sneaked out whilst Mimmi wasn't watching.

"She's going to kill us for not saying goodbye properly," Ondina sighed.

"She can't come, I don't want anything to happen to her," Zac said as they walked to Rita's pool.

"Oh, so it's okay if something happens to us?" Nixie asked, jokingly. "I am the one with the moon ring." She held the ring up. Lyla had given it to her the day before. "Boy, I could turn you into a fish!!"

"The Moon Pool already did that, so you missed your chance," Zac joked at they reached the edge of Rita's water pool, with an underwater tunnel that lead to the sea. "Ready?" He asked his friends.

Ondina, Nixie and Emma looked at each other and nodded. "Ready," they confirmed together.

Zac smiled. "Then let's go."

They all swiftly dived into the pool in unison, flipped their tails, and headed for Mako Island.

Zac was in front, and the other three mermaids were behind him. When they got to Mako Island they swam to the beach and managed to pull themselves up to the sand. When they were far from the sea and the small waves, they dried their tails (except for Emma, who didn't have the heating power, so Ondina did Emma's for her) and, when their tails had fully dried and their legs appeared, Zac lead the way to the Merman Chamber, acting a lot more confident then he felt.

"Are you okay?" Ondina asked him. "Is the Chamber, like, calling you?"

"Calling him?" Nixie repeated. "As in: Hey Zac, I'm the Merman Chamber. Come visit me on Mako."

"Not like that," Ondina rolled her eyes. "Zac once had a connection to the Chamber."

"The connection must have broken after we destroyed the first trident stone and shut the Chamber down," Zac said. "I can't feel a thing."

But Zac was lying. A small part of him was making him want to go to the Merman Chamber, but not to save the mermaids and defeat Erik, but to do the opposite...

Zac still felt a connection to the Chamber, it was like it was calling to him. The Chamber knew he was a merman, and the Chamber wanted him to activate it...

Zac tried to push these thoughts to the back of his head. For a long while, Ondina had trust issues with him, and he didn't want her to find out what he was thinking, and bring those feelings of hate back.

"This way," Zac said.

"Ahh, the way to the volcano?" Nixie asked. She had never been to the Merman Chamber before. Neither had Emma.

It had just started to get dark, and there was a chill in the air. Everyone shivered in unison.

"We need to destroy the stone," Emma said. "Maybe that will break the connection that Erik has with Sirena and Bella."

"Then once we sort that out he'll have to give Cleo back," Nixie nodded in agreement.

Zac lead his mermaids friends to the rock wall by the volcano.

"We're here," he announced.

"Where's the door?" Emma asked.

"The door can only be opened when the full moon passes over the moon pool," Zac sighed. "And the moon hasn't even risen yet."

Just then, to everyone's amazement, part of the volcano wall disappeared, revealing a pathway inside!

"How-?" Everyone turned to find Nixie, Sirena's moon ring on her finger, holding the ring up to the door.

"The door can only be opened by the full moon, or something that holds the power of the moon," she smiled.

"Nixie, you're a genius!" Ondina cried. "I completely forgot about that!"

Nixie smiled, pretending to examine her fingernails. "I do my best."

Zac, Ondina and Emma ran inside, and then Nixie sprinted after them, and the door closed just behind her.

"How do we get out?" Emma asked.

"When Erik comes we have until the full moon passes over the volcano to fight him and escape," Zac said.

Zac then lead the way to the Chamber. Erik, Charlotte and Dr Denman (and Cleo, Sirena and Bella) were nowhere in sight.

"Whoa..." Nixie and Emma whispered together, looking around the Chamber.

"Erik mustn't be here yet," Ondina said, looking around as well.

"He'll come," Zac said. "I'm sure of it."

"And you are correct," said a voice in the shadows.

Everyone turned to look, and there was Erik and Charlotte, walking towards them. Erik was holding his massive moon stone in his hand, and he was tossing it up and down carelessly.

"Erik," Zac snarled.

Erik grinned. "Nice to see you again, Zac. Last time we had a proper conversation you fell onto a table!"

"I didn't fall, you pushed me," Zac corrected Erik.

"I didn't even touch you," Erik told Zac.

"You used your magic," Nixie gave a small eye roll, and walked forwards to stand next to Zac.

"And now we're all here!" Erik held his arms out, presenting the Chamber. "Do you like my chamber? It's where I've been loving for the past few months."

"This isn't your Chamber," Zac said. "It was made by my ancestor. It belongs too me."

"And when you had the chance to start it up you didn't bother!" Erik reminded Zac. "This chamber was built for mermen. It's my chamber just as much as it is yours."

"Erik, please," Ondina tried, walking forwards and standing next to Zac. "You don't know what you're doing."

"Doesn't he?" Charlotte asked. "It kind of looks like he does to me."

"It's not too late, Erik," Emma tried, standing next to Nixie. "Give us the Moon Stone, we can turn it back into the smaller stones for the rings again, and we can all live in peace."

"Don't listen to them," Charlotte commanded Erik.

"Do you really think I'd leave you for them?" Erik asked Charlotte, who smiled.

"We don't want to have to use magic against you," Zac said, slowly raising his arm. "But we will do, to defend Mako Island, and all the mermaids."

Emma and Ondina and Nixie all raised their arms too, their hands pointing at Erik, ready to strike magic at any moment.

Erik gave a small laugh, but stopped, and looked up. Everyone else did too, and they saw the ceiling of the Chamber. It was showing the night sky, and the moon was just starting to appear.

Erik grinned. "Finally, it's time."

He pushed past Emma and Nixie and walk to the pedestal and waved his hand over the symbols in the correct order. Zac ran up to him and grabbed Erik, pushing him backwards. Erik fell and dropped the stone. Zac grabbed it.

"Nixie!!" He yelled, holding it up.

"Don't throw to me!!" Nixie cried, trying to fight Charlotte, who was trying to tackle Ondina to the ground. "When a mermaids touches the trident stone she loses her powers and the life of drained out of her!"

"This isn't the trident stone!!" Zac reminded her.

Nixie paused. "Oh yeah!!" Nixie held up her hands. "Pass it to me, I'm open!!"

Zac threw it to Nixie but, out of nowhere, Dr Denman appeared and caught it.

"Ha ha!!" She yelled excitedly.

Erik jumped up. "Good one, Linda!!" He grinned.

Emma ran up to Dr Denman, but Dr Denman held the stone out of reach. "You better be careful," she said. "If you try attack me, who knows what would happen to Cleo?" Dr Denman pointed.

Everyone looked where the scientist was pointing, and there was Cleo, in her mermaid tail, lying on the ground. She looked up. "Emma!!"

"Cleo!" Emma gasped.

Dr Denman walked up to Cleo. "Wouldn't Cleo look absolutely lovely in a fish tank in my upcoming science show?"

"You wouldn't dare," Nixie growled.

"That's the thing: I would!!" Dr Denman laughed.

"Girls," Erik called into the shadows. And Sirena and Bella appeared. They looked tired, but they still smiled with a glint of evil in their eyes.

"Yes, Erik?" Sirena asked.

"We'll need your help defeating these imposters," Erik said.

Bella smiled. "Certainly."

Erik looked up, the moon was almost half way across the screen on the ceiling.

"You may as well give up," Erik addressed Zac. "There are five of us, against four of you. Plus we have more magic."

"Correction, there are five of you, but eight of us," said a voice coming from the Chamber. There was Rikki, awake, and looking so much better, with Evie, Lyla and Mimmi just behind her. "Nine, if you include Cleo. Which I do. So there's five of you, but nine of us."

Erik narrowed his eyebrows. "Hmm..."

"You may as well give up," Mimmi said to Erik as she walked over to Ondina and Zac.

"Don't do something you may regret, Erik," Evie said, walking to Zac and taking his hand.

Rikki sneaked around everyone and began to steam dry Cleo's tail with no one noticing.

Erik snarled. "We can easily beat you, get the Chamber up and running and leave the Chamber before the full moon passes."

"I wouldn't count on it," Lyla smirked.

Dr Denman (still holding the huge moon stone), Charlotte, Sirena and Bella stood around Erik.

Cleo, Emma, Rikki, Evie, Lyla, Nixie, Mimmi and Ondina stood with Zac on the other side of the Chamber.

"Let battle commence!!!" Rikki threw her arms in the air.

The final battle had officially begun...