As Bloom, Flora, Nereus, and Serena pursue Tritannus, the rest of the Winx and their allies defend the Pillar of Light from Tritannus' mutant merpeople army. Bloom has Flora remain behind to help them while she and Nereus go after his brother. Tritannus had also taken Aisha prisoner to use his cousin's Sirenix power to activate the Emperor's Throne.
At the throne, Tritannus locks up Aisha with Daphne and activates the throne. As he's imbued with the throne's power, it causes him to grow and become more malevolent, but it also causes him to lose all reason of common sense or smarts, turning him into a power-hungry monster as he even attacks Icy, who is saved by Darcy and Stormy, but a combined attack from the Trix is no match for Tritannus, and he blasts them away to parts unknown in the Infinite Ocean.
Meanwhile, Tritannus' power boost causes his mutant army to stop fighting and head for Andros, being pursued by the rest of the Winx and Princess Tressa, along with the Winx's Selkie partners. At the palace, Aisha's parents, King Teredor and Queen Niobe make their way to the highest turrets of the castle to escape the rising waters, but when they find themselves trapped and confronted by some of the mutant mer-people, the Winx arrive to rescue them and Stella provides a means to transport them to safety for the time being before the palace is completely underwater. The Winx soon head to reinforce Roy and the mermaid guards who were severely outnumbered by their mutated brethren.
Back at the Emperor's Throne, Bloom and Nereus are having a hard time with Tritannus, until they realize that if they destroy his trident, his powers will be destroyed as well. Nereus manages to disarm his brother of his weapon, and Bloom destroys it with her Sirenix spell before Tritannus can reclaim it. With his trident destroyed, all of Tritannus' pollution-induced spells are undone: Aisha and Daphne are released from their bonds, the two mutant guards turn back into Queen Ligea and King Neptune, allowing Nereus to reunite with his parents, and all of them confront Tritannus as he grumbles at having killed them all when he had the chance before reverting painfully back to his merman appearance.
On Andros, the mutants also all revert back to normal and the water levels recede back to their original state. Teredor and Niobe reunite with their subjects, and soon are reunited with Neptune and Ligea, to a tearful Tressa's joy. Soon, all eyes are on Tritannus as Nereus asks his humiliated brother if he has anything to say in his defense. When Tritannus retorts snidely that he should have killed them all when he still had the chance, Teredor and Neptune disown him and banish him to the Gate of Oblivion for eternity, much to Tritannus' horror.
As the former Prince is escorted by two restored merman guards and the Winx to the Gate, Aisha has no remorse for her cousin's fate, deciding it is what he deserved for all the grief he's caused their family and the Magic Dimension. Tritannus is forced through the Gate, whimpering and shouting all the way. Afterwards, Bloom's Sirenix Guardian appears to grant her Sirenix wish, and Bloom wishes to break the Sirenix curse that had plagued her sister Daphne for so long. The wish is granted, and Daphne is restored to her flesh and blood form, reuniting with Bloom at long last in a tearful embrace.
Later at Andros Palace, many guests from around the Magic Dimension, from royalty like King Oritel and Queen Marion, to Bloom's foster parents from Earth, Mike and Vanessa, come together as it is announced that every planet in the Magic Dimension will now stand united as one family, before the Winx appear to perform a concert, ending with Bloom flying over to Daphne, sharing a hug with her and both sets of their parents, birth or adopted, and dancing together to end the season.
This episode provides examples of:
- Big "NO!": Tritannus shouts one when Bloom is about to destroy his trident.
- Breaking Old Trends: This marks the first season finale of the series where no onscreen kisses between the Winx and the Specialists occurred.
- Back from the Dead: With the Sirenix Curse broken, Daphne is finally restored to her physical form.
- Make a Wish: Bloom earns her Sirenix Wish, and uses it to break the Sirenix Curse once and for all, restoring Daphne to her physical form.
- Oh, Crap!: Tritannus' reaction when his choice of words in his defense result in Teredor and Neptune banishing him to the Gate of Oblivion as his eternal punishment.
- The Unapologetic: Tritannus refuses to own up to what he did, instead feeling sorry for not destroying the family when he had the chance. As a result, he is banished to Oblivion.
- Void Between the Worlds: Tritannus is banished to Oblivion as punishment for what he did.
- What Happened to the Mouse?: Musa never used her Sirenix Wish.
- In addition to that, what happened to Politea, who was supposedly kidnapped by Stormy and Darcy when they took her powers?
- The third movie reveals she was turned into a Nymph.
- In addition to that, what happened to Politea, who was supposedly kidnapped by Stormy and Darcy when they took her powers?
- Wham Episode: Tritannus is banished to Oblivion, Teredor and Neptune end their longtime feud, and the Curse of Sirenix is broken for good, restoring Daphne to her physical human body.
- You Have Outlived Your Usefulness: Tritannus gives this to Icy after powering up from activating the throne, coldly turning on her and not wanting her as an empress anymore as he promised, and that he can rule all oceans himself.
