A/N: I got this idea from Flaresouth, and their book "A Wish on a Full Moon"! Go read their book too, it's really good!
Ms. Chatham had always told them to embrace magic, but as the full moon approached the girls could feel that magic was not to be messed with. That may be one of the reasons giving up their powers to stop Denman felt so wrong. The girls felt like they had become mermaids on purpose, as if it was meant to happen to them. They weren't just some girls who fell into the moon pool and turned into part-time fish. They knew that magic chose them for a reason. So going against magic, for however good of a reason, seemed wrong.
Ms. Chatham said that giving up their powers would protect them from Denman, but the girls knew they wouldn't feel the same afterwards. They had grown into these new people, intertwining themselves with their identities. Rikki had learned how to let people in, and trust them. She learned how to let herself be loved, and keep her friends close. Emma learned how to relax, and go with the flow. Being a mermaid taught her about life's unpredictability, and how to live in the moment. And Cleo learned confidence, and to have trust in herself. Cleo's fear of standing out was shattered by her fishy lifestyle. She finally learned to be content as herself.
While the girls knew that as they entered the moon pool once more to give up their tails, they weren't directly giving up their personal growth. But the progress they'd made as people was the direct result of living as mermaids. But regardless of their fears, the girls knew that the only way they'd be safe was if they followed 's advice. So, faced with only the choice of giving up, the girls made their way to the moon pool.
The girls walked into the moon pool cave single file, with Emma at the front, and Rikki bringing up the rear. Denman's equipment was left scattered and abandoned surrounding the moon pool, but the place looked deserted. "I much prefer swimming in," Cleo says sadly.
"And if Denman had set more traps underwater?" Rikki countered. "Looks like she's given up," Cleo replied. Emma chimed in "She's not the type, Come on." Emma walked right up to the edge of the moon pool, with the other girls a few paces behind her.
The girls look up as they see the full moon about to pass overhead. "The moon's nearly overhead now," Emma says softly. Rikki looks down from the moon to the water, saddened by her future outcome.
"Funny, I… thought this would last forever," Emma says without breaking concentration on the moon pool. Rikki looks at Emma and Cleo, and the girls join hands. "What will you miss most?" Rikki asks. Emma pauses, and then replies. "I'll miss surfing without a board."
Cleo also hesitates before answering, "I'll miss how I could make water do anything I wanted. That was great."
Rikki nods, "I'll miss how cool it all was." Each girl gives a sad smile, but something quickly distracts them. A large air bubble rises to the surface of the moon pool, and Cleo worriedly looks to Emma. "Is that supposed to happen?"
Dr. Denman and two of her assistants rise to the surface of the moon pool. The girls step back in confusion, dropping their hands from each other's grip in the process. Denman swims to the edge of the pool to get closer to the girls, "Stay right where you are." She steps out of the pool, and puts her hands up in a deescalating manner. "We don't want to have to hurt you."
The girls step apart, and prepare to fight. "I wish we could say the same," Rikki says with a nod of her head. Cleo reaches her hand up, and begins to grow a large water tentacle from the moon pool. She shoves it in the direction of an assistant, blasting him to the ground. The second assistant gets out of the water, and Emma aims her powers for him. She freezes his wetsuit, and he becomes immobile. They girls then turn to Denman while holding their hands up, ready to take her on for the last time.
"Enough!" Denman says sternly. "Ok?" she says more softly. "I want you girls to consider an offer."
Emma quickly intervenes, "It's too late." They drop their hands and turn back to the moon pool, looking up as the moon finally passes. Denman follows their eyeline confused, and then looks down at the pool as it begins to change. Emma grabs for Cleo's hand, "It's time." All three girls join hands, and look at Denman with disgust. "We're giving our powers up."
"When we enter the water, we're giving up everything," Rikki adds. Denman looks at the girls in sheer confusion, baffled as to why the girls would make this choice. "But why would you give up being mermaids?" She asks, presently more confused on why they would give it up, rather than how.
Cleo looks at Denman with resentment, "Because of people like you." Emma joins Cleo in a look of condemnation, while adding "There will always be people like you trying to exploit us. The only thing left to do, is to give this all up."
Denman becomes desperate, and tries to bargain with them. "No, you can't." Rikki, Emma, and Cleo begin to walk to the moon pool. Cleo quickly looks away to answer Denman, but then focuses back on the water, "Yes we can."
"Please, if we work together-" Denman says frantically. Rikki shakes her head, "Not interested." Cleo and Rikki look to Emma, and then in a non-verbal agreement, step into the water. The girls splash into the water, and come back up to the surface as mermaids. The bubbles that once transformed them into mermaids begin to reverse their magic, and the girls look down at their tails for the last time. The moon moves almost entirely into the earth's shadow, about to block out all the moon light.
"You can't do this!" Denman shouts one last time. Just as the moon is completely covered but the shadow Denman shouts, "We have to know. We all have to know!" An incredibly bright light comes from the moon as it passes through the shadow to the other side, and Denman has to hold her hand up to protect her eyes. But instead of the light dying down, it only gets brighter. The cave begins to spin and the light gets so bright that nobody can see anything but white. The spinning begins to wind down, but they do not return to the moon pool. Not on Mako, not on the mainland. No where they've ever been before.