Somewhere out on the ocean floor, Nixie sat by herself alone in the reef. She has been so horrible to her best friends and she is feeling bad about it since they kicked her out of the cove. While looking down at the sea flowers, Nixie thought about the time when she was a little merchild. Her parents were killed by a giant leviathan, leaving her to be an orphan. She had a hard experience growing up throughout her life. At the age of ten, she was bullied by other merchildren, even the royal ones who are the perpetrators of this bad situation. They are the worst. They will always look down at Nixie and they'll belittle her to no end. Which is why she is led to believe that people who are born in royal blood are the vilest pigs ever to rule every land in the world. Sometimes it's not always the case. During those dreadful times, she has befriended Isabella at a young age as well as the other mermaids, Taliah and Lee Lee. When the royal bullies berated Nixie the next day, Taliah, being a strong African little merchild, stood up to the bullies in her defense. Though she is to be thankful that she had them as her friends, the sad experience still had took its toll on Nixie's personality, making her into a edgy, emotional, rebellious, carefree mermaid that she now is today. Instead of being thankful for what she had, she was very mean to everyone else in a way the bullies were to her long ago. She was so nasty to her best friends at the secret sanctuary. The only mermaids who truly accepted her. They will always had her back and in return, she spewed her harsh words towards them and everyone else inside the secret sanctuary. Now the final straw has been made when she let's her hatred towards royals blind her sight and she went behind their back, telling Akauriana's father about her with the prince. That result made the little mermaid swam away. The edgy black haired mermaid felt so terrible like she is a worst enemy not just to herself, but to her best friends as well. If only she can take back everything she has ever done, especially towards Akauriana, they would have forgiven her. As she sat there quietly with her thoughts, suddenly a black inky mist hovers over the reef, blocking the sunlight. Nixie looks up to notice the dark mist. She knew that something is not right when the dark inky mist is heading towards Mermaidiana. Without hesitation in the slightest, Nixie summons her courage to follow the mist from behind. While at the foot of the kingdom grounds, Nixie hid amongst the coral, wondering about what's going on with the mist. The edgy mermaid gasped in horror as the dark inky mist flickers with lightning followed by the sound of thunder. Then the mist revealed the large eyes of Eraza. This sight of it terrorize the mer-people who gazed upon the monstrous mist. The guards quickly informed King Aquarion of the mist and he swam outside of the palace to glare at it. He knew it had to be Eraza, the minute she called him out.

"King Aquarion!" Eraza bellowed in a demonic voice. "Come out of your castle and face me! If you fail to comply, you'll never see your daughter again!"

The king is alarmed by her threat. The sea witch has Akauriana imprisoned within her grasp. He immediately went to grab his trident from his throne and he is on his way out to save his daughter. The grandmother rush to her son's side for she has feared that the worst could result in losing more than her granddaughter.

"You mustn't go out there!" the grandmother says out of worry. "The sea witch has planned for your disposal all along."

"I have to, mother." said King Aquarion. "She has my daughter. I have to go and face Eraza."

"It could be a trap!" said the grandmother out of fear as she tries to stop her son from making a mistake of his life. "She's using your daughter as bait. There has to be another way!"

"What if there isn't!?" King Aquarion says in concern, facing the grandmother. "I'm sorry, mother. But this is the only way I can save Akauriana. I have to do this."

The king turns to the doors opening for him. With the trident ready in his hand, King Aquarion bravely faces the unknown.

"You're right, mother." said King Aquarion strongly. "I've lost my beloved queen Merella. I'm not going to lose my daughters too. Especially not Akauriana. Please watch my other daughters for me."

The king swims out to the open waters. The grandmother watches him leave, hoping for her son to be okay and bring Akauriana back home safely. While out on the outskirts of the ocean floor, King Aquarion swam to the gapped valley. He finally has arrived at the trenches of the sea mountains where Eraza is waiting for him.

"Here I am, Eraza!" shouted King Aquarion.

"You're right on cue, Aquarion." grinned Eraza, turning to face him.

"Where is my daughter!?" the king demanded.

"Right here!" says Eraza as she points to her henchmen.

The mutant eel men has appeared before the two. The muscular brute eel man has held onto Akauriana in his strong hands. She is now turned back into a mermaid again. Terrified for her, King Aquarion rush over to her but the strong eel man pulled her away from him. Akauriana looks at her father with fear. She couldn't speak to him without her voice, which made the king even more furious than before. He glares at the sea witch.

"Her voice! What have you done to her, Eraza!?" King Aquarion scolded.

"Nothing!" said Eraza in a eerie pitch. "She's done it all to herself! Trading her lovely voice away and for what? A human heartbreak?"

Enraged, King Aquarion powers up his trident and aims at Eraza.

"Let her go!" King Aquarion demanded.

"Not on your life." snickered Eraza as she orders her spike haired eel man to aid her. "It so happens that your daughter has signed the contract."

The eel man shows the scroll to prove that Akauriana had signed her soul away to Eraza. King Aquarion was shocked to find her name, in her signature writing style, imprinted on the bottom. Eraza manipulated the king by striking a new deal.

"She even drew a little heart above the I." says Eraza, going in riddles. "Is it binding? Oh deliciously yes! Unbreakable, impenetrable and even indistinguishable! Unless?"

"Unless what?" King Aquarion asked, puzzled.

"There is a little something I'd be willing to try." says Eraza.

"Go on!" said King Aquarion.

"Oh yes I shall." said Eraza as she continues her manipulating riddle. "Perhaps we can make a exchange. How about I swap your daughter's soul for your own?"

"What!?" said King Aquarion in shock. "My soul!?"

"Yes, your soul!" says Eraza as she urges him to sign the scroll. "Now sign the scroll and set your daughter free. Or else I will take her with me, to suffer through eternal darkness all alone!"

Eraza swam up to pinch the little mermaid's cheeks.

"Just look at her, Aquarion!" teased Eraza. "She is nothing but a mute little hatchling, drowning herself into her own sorrow with no voice left to cry out your name."

Nixie peeked out through the boulders. When she sees Akauriana captured by the scary tough eel man, Nixie was terrified for her. Now she feels even more worse about her bitterness towards Akauriana. The black haired mermaid continues to observe the dreadful situation as Eraza awaits for the king's decision.

"Well I'm waiting." Eraza teased slightly.

"It's not my soul you are after." said King Aquarion as he figured the witch's riddle out. "It's my power! My throne and my kingdom!"

"Which would you rather be, old man!?" snarled Eraza. "The king of the sea? Or a father to his little girl?"

Defeated, King Aquarion looks at Akauriana who is shaking her head, urging him not to do it. For her sake, the sadden king have to give up his everything to the sea witch.

"I'm sorry, Akauriana. But I have no choice." said King Aquarion as he points his trident at the scroll, replacing Akauriana's name with his own.

Satisfied by his surrender, Eraza laughs for she has carried out her revenge. She uses her dark magic to gravitate the king's crown and his trident towards her. In her possession, the ink colored the trident black as well as the crown on her head. Akauriana watch in horror as Eraza turns to the king, who is now at her mercy.

"At last, it's all mine!" cried Eraza in triumph. "After all of these years, I have suffered miserably in the dark trench of the sea while you claimed what was once mine! But this time, the tables have turned! Now you'll see for yourself how banishment feels!"

Eraza zaps King Aquarion into a prisoner within a plant. Then she locked him inside the mountain. With the trident in her hand, Eraza reclaimed her status as the evil queen of the seven seas once again. Akauriana lowered her head in despair, knowing that her father has given up his power to free her from her fate. Eraza turns to face her henchmen and Akauriana with a wicked grin.

"Now I shall reclaim my throne like before." says Eraza, approaching closer to the brute eel man holding onto Akauriana. "And you, little mermaid, will have a front row seat and watch while I turn Mermaidiana inside out!"

The sea witch turns to her henchmen.

"Let today be known that all the kingdoms, all the oceans of the earth belongs to Queen Eraza!" the witch bellowed.

All of her terrifying henchmen cheered for her speech. Eraza leads her growing army towards the underwater kingdom.

"Now onward, gentlemen!" commanded Eraza, leading her men. "Time to conquer Mermaidiana!"

Nixie knew that she has to do something about this ordeal but she cannot do it alone. The magenta tailed mermaid swam out of the rocks and out to the ocean floor in order to get help. Meanwhile upon the surface, Tristan rowed the boat out to the open waters. As Isabella told them everything, Prince Dominick and Princess Daphne were completely stunned by the information. The two royals are appalled of what she and Akauriana had to go through just to be with them. Daphne doesn't know what to feel about this. After all, she has thought that things were meant to be when she was to marry Prince Dominick. Now she felt confused entirely of her role in this situation. Prince Dominick, on the other hand, is just a shocked as Daphne when they heard the whole story.

"So let me get one thing perfectly clear so I don't misunderstood you." Prince Dominick remarked as he tries to wrap his head on this one. "Akauriana is a mermaid, just like you are, who happened to save me from a shipwreck on the stormy sea?"

"Yes, that's right." says Isabella, nodding her head.

"And she gave away her voice to become a human, all just for me?" asked Prince Dominick.

"Yes she did." said Isabella.

The young prince turns to the bounty hunting pirate who is rowing the boat.

"You also knew about this too?" Prince Dominick asked Tristan.

"Aye! I've only met Isabella in her mermaid form days before." said Tristan. "To be honest, the sea witch part did kinda throw me off guard right there."

"So this sea witch, Eraza used the both of you for getting revenge on the sea king?" Daphne asked Isabella.

The floral mermaid nodded sadly in which is pretty startling for the princess.

"She sounds like a real monster." said Princess Daphne.

"She truly is a monster." said Isabella with a strong expression. "If we don't do something about it, the mer-people will be doomed."

"How are we going to do that?" Daphne wondered. "None of us can't breathe underwater."

"Perhaps not us, but you can, Isabella." remarked Tristan as he crept closer to her. "You have a to go help your friend."

"But Tristan?..." uttered Isabella.

"We all have to stay up here." said Tristan, touching her face. "It's where we human beings belong. We're not going to be much helpful down there. But you, Isabella. The sea is your turf. You have to go do this."

Isabella hugs Tristan and he returns the favor, holding her in his arms. Prince Dominick and Princess Daphne were touched by their heartwarming moment. Now the question is, how is Isabella going to help Akauriana if she's human? Luckily for her, Paulina and Will had surfaced, only to find that Isabella is a human. They are briefly shocked by this sight but they cannot pause for another minute, because Eraza is already making her move on Mermaidiana. After Isabella explained herself to them, Paulina had an idea. She dove under the sea and swam to the secret sanctuary, to ask the sea pixies for help. They all agreed to make a magical potion out of their pixie dust. Then Paulina took their vile to the surface, where they've awaited for her arrival back. The colorful parrotfish hands the potion to Isabella.

"What is it?" Isabella asked, wondering.

"It is a potion that the sea pixies have made." said Paulina. "If you drink their brew, your tail will grow back."

"That means you can come back to help all of us!" exclaimed Will.

Isabella glances at the glowing potion and turns to Tristan, Dominick and Daphne before she can face the sea.

"So if I drink this, I can become..." Isabella utters softly.

"A mermaid again!" exclaimed Paulina.

"Yes, but we must hurry!" Will added in concern. "The sea is not going to save itself."

Without hesitating in a slightest, Isabella drank the potion and undergoes a magical transformation. Prince Dominick and the other two witness the phenomenon of a extraordinary discovery when Isabella's true form is revealed. Tristan smiled for he already knew what she must do. The girl's legs fused together to form a long shimmering fishtail. When the transformation is complete, Isabella is a flower mermaid once again. She dives into the water. Along with her friend swimming by her side, Isabella swam to the secret sanctuary. Upon her arrival, Taliah and Lee Lee was relieved to see her again. Though they were upset about her not telling them where she went, Isabella apologized for her reckless decisions. She can make it up to them later. The floral mermaid has told them everything they need to know, even the sea witch's plans. Taliah has a plan of her own. She went to far ends of the sanctuary, to inform the bigger creatures that protected this cove of Eraza's plans to poison the sea with darkness. The strong male creatures were not happy of the news for they have hated the wicked witch. So they agreed to help the mermaids and the other creatures in the secret sanctuary. They all form a huge alliance overtime. Every rare race of sea creatures, big and small, gathered together to hear what Taliah had to say.

"Thank you all for coming to hear me out!" Taliah speaks out to continue her speech. "Y'all are wondering why you're here! Allow me to tell you! One of my best friends have some information on the dreadful situation that is happening now as we speak! I'm sure everyone here has heard about Eraza the sea witch, am I right?"

All of the creatures growled in pure disgust and disbelief. They haven't forgotten about the time when Eraza was the queen of Mermaidiana years ago. Taliah continued to explain the details Isabella has shared with her and Lee Lee.

"Well not a minute ago, Eraza is on the rise for power!" announced Taliah as she went on. "She has princess Akauriana, who is now her prisoner. That's all Isabella can share with me. But we all know that it is far from over. This is why I'm asking all for you for help! If Eraza isn't stopped, she'll become even more powerful than before and then what's next!? She will poison the entire oceans unless we find a way to stop her! Not only for our sakes, but for my friend Akauriana and all of our friends from this sea to the other! This may not going to be an easy fight, but the fate of the sea rests in our hands now! Now let's go stop ourselves a witch!"

The creatures bellowed with each their own strength. The mermaids lead their aquatic allegiance out of the sanctuary and is now headed towards the open sea. While they're out in the open, they happen to run into Nixie. She also has a army of strong marine mammals of her own. She is happy to see them, even though they still haven't forgiven her for her actions.

"Hey, you guys!" greeted Nixie out of joy. "Look! I'm sorry for the way I acted towards everyone, especially Akauriana. Can you ever forgive me?"

Taliah swam up to her and smiles.

"Of course, Nixie." said Taliah. "You can make it up to us when we stop the sea witch."

"I know where she is." says Nixie as she points out northeastward. "She's at the castle! With Akauriana as her prisoner! And oh boy! What she has done to Mermaidiana is not pretty!"

"Oh no!" shrieked Lee Lee in fear. "That witch has already taken over Akauriana's kingdom? That is so mean!"

"Now the mer-people are in danger!" shrieked Isabella. "It won't be long before Eraza can blackout the whole ocean!"

"Then we have to go now!" shouted Taliah as she turns to Nixie. "Lead the way, Nixie."

"You got it, girl!" Nixie replied as she takes the lead. "Follow me, everybody!"

She led the army of rare sea creatures towards the kingdom of Mermaidiana. Meanwhile, inside of the palace, Eraza redecorate the castle into a terrifying shade of black ink. She imprisoned the royal family in the dungeons below the castle's reefs. She has placed Akauriana into a special dark crystal prison on the western wing of the castle. With Mermaidiana in her clutches, Eraza admired herself in the mirror, decked out in her hellish accessories. She dazzled in her dark jewelry. During her admiration, the mutant eel henchmen came to the throne room, informing her that the creatures of the secret sanctuary is waging war on the horizon.

"Well where are they?" the sea witch demanded for answers.

"They are coming from the outskirts on the ocean floor." said the big brute eel man. "They're coming in massive numbers, my queen."

"And they are being led by those little mermaids who were friends with the youngest princess." said the spiky haired eel man.

"Interesting!" said Eraza, turning to the window. "Who knew she had friends from somewhere else. Perhaps quite a lot of them."

"You're not worried, my queen?" the third bald eel man questioned the sea witch.

"No! I'm not worried." says Eraza with a strong expression. "Nothing worries me."

"But they are coming here, my queen!" warned the bald eel man.

"Then let them come." Eraza said in a strong wicked tone. "Let them bash their heads on the blackened stone walls. Then and only then, shall they learn of their place."

She commanded her henchmen to prepare her army of the most terrifying hybrids of the sea for battle. Out on the foot of the kingdom grounds, the young mermaids led their army of the rarest sea creatures on top of the boarders edge. They noticed that the sea witch has a army of her own. The scariest dark hybrids created by her malice. Most of the good creatures were afraid for their lives while others stayed strong and proud to face their fears. There is no turning back for every one of them now. Taliah took charge like a strong young mermaid.

"For Mermaidiana!" bellowed Taliah, commencing the attack.

"FOR MERMAIDIANA!" all of the creatures bellowed with her as they followed her lead.

They all clashed with the dark hybrid creatures within the kingdom. The battle had just begun. With the strong ones helping out the vulnerable fishes, they overcome the first wave of the army. Now they have to push through even the mightiest of them all. While the strongest creatures takes them on, the young mermaids slipped their way through the battleground. The majestic whale sharks covered the girls as they helped the endangered merfolk and make sure they are safely out of harms way. Nixie fought off the scary creatures that are terrorizing the helpless mermaid family. Lee Lee darts through the reefs as fast as she can, luring away the group of monstrous sea men that are chasing her. Taliah helps the strongest male creatures push back against the malevolent enemies. Isabella, alongside with Paulina and Will, swam over to the castle. She notices Eraza watching from the window above. The sea witch also notices her from the battleground. Then she turns away from the window. One of the biggest creatures tried to eat Isabella and her friends. But this just in, the titanic merman tackled the monster, saving the floral mermaid's life.

"Thank you!" shouted Isabella thankfully.

"You're welcome!" the titanic merman responded strongly. "Go inside the palace! I'll cover you!"

As the huge merman fought the sea monster, Isabella and her friends heads inside the palace. They swam through the dark passageway in which led them the dungeons of the castle, where Eraza has kept her prisoners. While swimming along the way, Isabella immediately knew the royal family when she spotted them in the dungeons ahead. She swam to the mermaid sisters whom were being held inside the prison above their grandmother's cell.

"Are you all okay?" asked Isabella.

The mermaid sisters has noticed her, hovering before them.

"Who are you?" asked Ondina.

"You all may not know me but I'm a friend of your sister." says Isabella.

"So you're one of Akauriana's friends!" exclaimed Coralline, swimming to the bars.

"I'm here to help you, your majesties." said Isabella.

"How? The bars are too strong." Leah wondered.

Luckily for the princesses, Will recruited three strong sharpshooter fishes to break the cell with their strong snout. At last, the mermaid princesses are free. Now they have to free their grandmother from her cell. With the help of those strong rare fishes, they freed the king's mother. They all cheered for their freedom but Isabella cannot pause. She knew that one of the mermaids remains missing from the scene. The floral mermaid turns to the grandmother of the royal girls.

"Where is Akauriana?" Isabella asked the old lady.

"If I must know, the sea witch had imprisoned my granddaughter in the west wing." the grandmother replied.

"The west wing?" she wondered.

"Yes, my dear." said the grandmother. "That's where she's holding her. My poor sweet child."

"The west wing is right above the castle." says Starmy as she pointed Isabella in the right direction. "Take the passageway on the left. That'll take you straight to the west wing."

"Thanks, your majesty." said Isabella, nodding respectfully as she leads her friends. "Come on, you guys!"

"Coming!" replied Paulina, swimming behind Isabella.

"Right behind you guys!" replied Will, tagging after them.

"Where are you guys going?" questioned Mya.

Isabella turns to glance at the royals.

"We're going to save your sister." Isabella responded with a smile.

"Be careful, child!" says the grandmother, worrying for Isabella's safety.

The sharpshooter fishes escort the royal family outside the dungeons safely. Isabella and her friends took the passageway that led them to the west wing of the castle, to free the little mermaid. From the outside, the battle between the dark sea creatures and the ones from the secret sanctuary continues to clash over the castle's reefs. During the fight, Taliah ask the other creatures to go help Isabella inside the palace. They went inside to aid the mermaid. The good creatures caught up with Isabella and her friends while they were soaring through the tunnels, swimming upwards to the west wing. They finally reach the top of the west wing, just like the sisters told them to go. What the brave youngsters now witness, stuns them with fear. Their princess Akauriana is trapped inside the crystals covered with ink, her body in suspended animation. Terrified, Isabella hurried closer to the crystal prison. She tries to break her friend free, but to no avail. Not even Will, Paulina and the strongest creatures could break the spell Eraza placed upon the crystal. It is too strong. The floral mermaid felt defeated for the final time as she wept over Akauriana's lifeless body from within the dark crystals.

"It's all my fault..." cried Isabella, sinking to the ground sobbing. "If only I could've been there for you, Akauriana. I was supposed to help save you from your fate. But now, I let my love for Tristan get in the way of our friendship. I am so sorry that I failed the both of you..."

Will and Paulina feel sorry for Isabella as well as the strong creatures. It really pains them to see the flower mermaid feeling so sad, defeated and distraught. She lowers her head down and cry, even though she can't cry tears underwater as a mermaid. Before all hope is lost for them now, without knowing it, Isabella quietly uttered the words that she'd held onto for a long time.

"Friendship is freedom..." uttered Isabella in sorrow. "And freedom is destiny..."

When she says those words, a sudden crack on the crystal became visible. Paulina notice this and so did Will. They informed Isabella that whatever she says those exact words that was once used for the secret sanctuary, is the key to Eraza's undoing by freeing the little mermaid from her prison. Now she knows what she has to do. She chanted the same words over and over again, until the spell has broken. The dark crystals shatters away and Akauriana's mermaid body is free. They wonder if she is still alive. To their relief, the little mermaid opens her eyes. Isabella hugs Akauriana in pure joy, knowing that she is okay.

"Oh Akauriana! Thank goodness that you're alright!" cried Isabella in relief. "I thought I'd never see you again. I promise I will never ever let you down again. We are in this together."

Akauriana tries to talk but then again, she still has no voice. Isabella also remembers that Eraza has her pendant as well. Now that she have everything in her hands, Eraza is more powerful than she ever was years ago. Feeling enthusiastically strong rather than to back out without a fight, Paulina swam over to the mermaids and she encourage them to fight, take back what's rightfully theirs. Isabella believes in Paulina's words.

"You're right, Paulina." says Isabella, feeling motivated by her parrotfish friend. "We can't just let Eraza win. Everybody is fighting for Mermaidiana! So we'll just have to do our best to stop her!"

She then turns to Akauriana.

"Don't worry, Akauriana." reassured Isabella strongly. "We will save your kingdom. Eraza won't get away with this any longer. If we fight back, then maybe I could get back my pendant that she took from me. And maybe we could get your voice back."

Akauriana nods happily with strength. As long as the rare creatures are by their side, they'll storm the castle in order to face Eraza. From the outside of the palace, the battle still continues. The three young mermaids reunited after they did their part of helping the other merfolk while the creatures fought back the dark hybrid ones. Taliah sees Akauriana and the others from afar. She also notice that the three mutant eel henchmen were trying to get them. Luckily, the bigger fishes was there to protect the little mermaid and her friends from the evil eel men, allowing them to proceed further in the castle. Taliah turns to her mermaid friends, urging them to hurry inside the palace walls. Nixie and Lee Lee acknowledge that as they follow Taliah inside the castle. A few creatures were too following behind the mermaids, leaving the battleground. Everyone knows that fighting against Eraza is not going to be easy but if nobody is to do something, all will be lost. Not just the oceans of earth, but all life as they know it. So they all have to act fast for it was almost too late.