Back at Gardenia, the Winx are preparing for one of their concerts. Their relaxing time is cut short when an oil rig off the coast catches on fire and starts polluting the ocean with gasoline. The Winx and Specialists manage to save its workers and prevent most damage, but some of the pollution remains in the water. During the mission, Sky loses the Pendant of Eraklyon, which he was going to give to Bloom. The one who loses it is said to never be happy with the one they love so this hits him hard.
In the ocean of Andros, King Triton is about to crown his successor. His son Nereus seems like the obvious choice, which makes his twin brother, Tritannus, angry. Nevertheless, that’s exactly what happens. Tritannus tries to kill his brother and father out of revenge but is stopped and imprisoned. From his cell, he absorbs the pollution that’s floating around and gets turned into a monster with amplified powers. This enables him to free himself and his prison neighbours, the Trix. He takes a special liking to Icy once they have met, and she returns his feelings.
To remain powerful, Tritannus must keep absorbing toxins. This leads the Trix and him to Earth where he recharges. The Winx face him but don’t know who he is due to his changed appearance. They also discover that their Believix wings don’t work properly underwater, which makes them slow and unable to fight well. Aisha recognises him just as he is helping Icy defeat the rest of the Winx. He once again weakens and escapes through a portal before she can do anything else.
A new school year starts at Alfea and the Winx return there. This time they are, once again, students. They speak to Faragonda about their new enemy, as well as the fault of their Believix powers. She instructs them to gain Sirenix, an ancient fairy power of the oceans. To start their quest towards it, they first must find the Book of Sirenix.
Since Daphne was the last fairy to Earn this power, Bloom asks her about the location of the Book. At first, she refuses to tell her. We learn that Sirenix is the reason that Daphne is a ghost. The three ancestral witches put a spell on it when they attacked Domino. Once she tried to use it, it turned her into a spirit without a body. Bloom persists and Daphne tells her that the Book is in the Magic Archive of Alfea.
During the search for the Book, the Trix appear in the Archive. The Winx and the Specialists fight them. During the fight, Sky falls off one of the floating platforms in the room and loses consciousness. When he wakes up he has amnesia and doesn’t remember Bloom or who he is, at all.
Tecna and Timmy write a piece of code used to search the Magic Archive. Meanwhile, Princess Krystal of Linphea tries to heal Sky with her powers, but the healing is blocked by something he doesn’t want to remember. That memory is the one of losing the Pendant. Tritannus learns of the Winx’s search for Sirenix and orders the Trix to stop them, while he finds out how to obtain it himself.
Tecna’s code backfires and she turns into a robot that wrecks the Archive, due to a Trix’s spell. Once her friends return her to normal, she is able to use it correctly and find the Book. The quest for Sirenix begins with the Book’s warning. The Winx must complete all the tasks to gain the power within one lunar cycle. If they fail, they will lose all their powers. They decide to proceed with the quest in order to stop Tritannus from conquering the Magic Dimension.
By accepting the quest, they each gain a Sirenix box which comes with a guardian of Sirenix who will help them with their tasks. They also gain Harmonix, an underwater power that will help them search the oceans of the Magic Dimension for the gems hidden within them before they gain Sirenix. They need to find the Gem of Self-Confidence, the Gem of Empathy, and the Gem of Courage in order to gain it.
The search begins in the oceans of Andros. To get there, Bloom, Stella, and Aisha use a yacht called the “Odyssea Explorer”. Their friends stay at Alfea and use the Simulator to help them find the gemstone faster. Aisha’s father sent a young man named Roy to accompany them on their journey. She is annoyed by his presence.
Each ocean of the Magic Dimension has a gate which is a portal to the other oceans. In the ocean of Andros, Aisha meets and bonds with Lemmy, the selkie who guards the gate of this ocean. She tells the girls that bonding restored her powers after Tritannus stole them. She also helps them get to the location of the Shimmering Shells, which are the key to continuing their quest.
When they arrive there, each of them must battle an illusion that is caused by the pollution left behind by Tritannus. The illusions attempt to destroy their self-confidence and by defeating them, Aisha, Bloom, and Stella prove themselves worthy of continuing their quest. As a reward, they receive a riddle pointing them to the next location they must go to.
Afterwards, they go to Solaria, where Tritannus has already drained the powers of the gatekeeper. As was the case with Aisha and Lemmy, Stella’s bonding with the keeper, Iliris, restores them. All members of Winx Club gain the Gem of Self-Confidence once Stella saves Aisha and Flora from a mutated jellyfish left by Tritannus. In the meantime, Sky remembers how to fight once he and the rest of the Winx battle the Trix who are polluting the ocean so Tritannus could use it to recharge his energy.
When the next riddle takes the Winx to Melody, Tritannus turns Musa into a monster. Bonding with her selkie, Sonna, breaks his spell. With the help of her Guardian of Sirenix, Musa solves the riddle. To gain the Gem of Empathy, the Winx have to go to Zenith. Tritannus places a spell on its location which makes them fight each other. Bloom avoids it and frees her friends from it. Together, they gain the second gem. As for the Trix; they manage to capture Daphne and torture her in order to learn how to obtain Sirenix. Despite the pain they inflict on her, she refuses to give them the answer.
The Ocean of Flowers on Linphea turns out to be one of the keys to the final gem, the Gem of Courage. In it, Flora, Musa, and Stella face the Flower of the Depths which has been corrupted by Tritannus. Being the fairy of nature, Flora frees it from his pollution. In turn, the Flower tells them the final riddle of the Sirenix quest will be revealed by the Book of Sirenix.
Since Daphne will not give them the answers to save herself, Tritannus sends the Trix to attack Bloom in order to scare her sister. Their plan to ruin the wind rider race at Alfea doesn’t work out, so they attack Bloom and Sky once they are alone in the Roccaluce Gorge. The two of them nearly lose to the Trix before the rest of the Winx arrives to help them. Once the Trix are gone, Bloom accepts that Sky may never remember who he was nor all the times they shared, despite being scared of it. What matters to her is that they make a future together.
On Domino, the Winx head to the Yellow Reef. To get the Gem of Courage, Bloom lunges into the jaws of a sea monster and snatches it up. Once she does that, the Winx have passed the three tests, but their quest is not finished. However, Bloom’s parents are attacked and nearly destroyed by the Trix. To try and save them, Daphne agrees to tell Tritannus how to gain Sirenix. The Pendant of Eraklyon has been found by Flora’s bonded selkie and returned to Sky. When he looks at it, he regains his memories and gives it to Bloom. He also tells her about Daphne being held captive by Tritannus.
By passing the final test and looking within themselves, the Winx find out the location of the Source of Sirenix. They go to Lake Rocalucce and earn the power of Sirenix. They also gain access to the Infinite Ocean.
Since he stole the powers of the selkies, Tritannus has access to the Ocean, as well. In it, he searches for the Emperor’s Throne. A structure that will make him more powerful. Upon finding it, he discovers it has been broken and that, to repair it, he needs the seals from the Pillars of the Infinite Ocean, each of which controls a concept in the Magic Dimension. He also empowers the Trix by giving them Dark Sirenix.
He manages to steal the seal of the Pillar of Light first. With the whole Magic Dimension thrust into sudden darkness, the Winx jump into action. After a fight with Tritannus, his mutants, and the Trix, Stella manages to restore it. The next to fall is the Pillar of Balance on Melody. Without the seal, earthquakes are felt through the Dimension. By using their Sirenix convergence, the Winx manage to restore it as well, saving the universe from total collapse. Upon seeing the mutual obsession between Icy and Tritannus grow, Darcy and Stormy leave them for fear of becoming their servants.
Before Tritannus can get to the Pillar of Control, Daphne contacts Bloom and tells her to destroy its seal. They do so and use convergence to stabilize the pillar once again. To replace the seal, Icy goes to find Politea, the nymph whose Sirenix power turned her into a monster, due to the curse of the ancestral witches. Darcy and Stormy beat her to it and take Politea’s power for themselves.
Without Politea’s Sirenix, Tritannus must find a replacement again. He attacks the Pillar of Light, once more, bringing an army of mutants with him. Princess Tressa and Prince Nereus call the Winx for help. Along with the selkies of all the oceans, they fight him and Icy. During the battle, Nereus dies and Aisha uses the wish which has been given to her by her Guardian of Sirenix, to revive him. However, she falls into her cousin’s trap. Tritannus seizes his chance and takes Aisha with him, stealing her Sirenix powers to activate the Throne.
Upon activating the Throne, Tritannus is even more corrupted. Despite his many promises and devotion to Icy, he casts her away from the Infinite Ocean, along with Darcy and Stormy who come to protect her. He sends his mutants to Andros and attempts to get rid of Aisha’s parents, his aunt and uncle. While the rest of the Winx fight the mutants to protect Andros, Bloom, along with Nereus, faces off against Tritannus. Together, the two destroy his trident and take away all his power, undoing all the harm he has done and freeing Daphne and Aisha. For his crimes, Tritannus is banished from the Magic Dimension and sentenced to cross the gate of Oblivion.
Bloom’s Guardian of Sirenix gives her a chance to make her wish because she has proven herself. She breaks the curse placed upon Sirenix. As a result, Daphne is no longer a ghost and is able to reunite with her sister.
Magical Memories Zine 