Friendship is the true magic!
Tritannus uses Oritel and Marion as bait to learn more about Sirenix from Daphne. With their three gems and the power of Sirenix at their fingertips, the Winx prepare to enter an incredible and new frontier as fairies.
The Winx Club are in the simulator as Faragonda, Griselda, and Palladium watch their training progress. Unfortunately, when the winx try to converge their Harmonix power, Bloom loses her concentration as she is worried about her sister Daphne.
In an unknown location, Tritannus still threatens Daphne to tell him her knowledge about Sirenix. Daphne finally gives up and tells him that her Sirenix powers are protected by the 'Source of Sirenix' in Lake Roccaluce. She tells him that he will never get Sirenix. But Tritannus has an idea to destroy the source itself and calls the Trix. Icy immediately realizes that Daphne has told Tritannus about Sirenix. Tritannus admits this and tells Icy that she will get Sirenix after Tritannus has it. Darcy wonders if she and Stormy would get anything and then Tritannus vows to Icy again that they will rule Magic Dimension together. While leaving Icy tells Darcy and Stormy to follow them, which makes Stormy angry.
Back at the dorm at Alfea, as the girls talk about Sirenix, worried that they might lose their powers. The Sirenix Book appears and tells them the last part (riddle) to gain Sirenix and then disappears for good, much to Stella's shock. After that Aisha suggests that they should go back to the Magical Archive.
After a long search in the Archive, Stella decides to ask her Guardian of Sirenix to help, but her Guardian only tells her to look inside herself like the book had already told. Flora admits that she is getting worried.
In the ocean of Magix, Nissa is playing with some Bollabies, telling them to line up, but then one of them turns into blowfish and starts floating up which makes Nessa a bit annoyed and she tells it not to go away by itself as it could be dangerous. While chasing it, the Ocean Gate of Magix opens and Tritannus comes through it, much to Nissa's shock. Tritannus ignores Nissa and heads to find the Source of Sirenix and finds it almost immediately from a cave. He stabs it with his trident, releasing pollution around it and draining its powers. As a result, the water of Lake Roccaluce starts to subside and the oil released from Tritanus' trident creates an oil-monster. Tritannus commands it to guard the cave in case the Winx would arrive and he flees only to be attacked by Nissa, Phylla, Lemmy, Illiris, Serena, Sonna, Lithia and Desiryee. Tritannus calls them "little squids" and fights back in order to destroy them.
Bloom figures out the solution for the last riddle, by realizing that the only way they can find the source of Sirenix is to look inside themselves and she communicates with her Guardian of Sirenix, who complimented the Winx and told them that they must go to the place where their quest began. The Winx realize that they have to go to Lake Roccaluce where their quest for Sirenix began to find the source of Sirenix. When they arrive with the Odessy Explorer, it stops because the water in the lake is getting drained. Tecna detects high levels of toxic in there, meaning that it is dying and the only person who could make this happen is Tritannus. Bloom gets worried about the Source of Sirenix and they transform into their Harmonix forms and dive into the lake. Upon entering, large amount of fishes swim through them as they are scared of the oil-monster created by Tritannus. As Bloom tries to block its attack, her shield breaks immediately and she is sent flying and when landing, she finds Tritannus and the Selkies fighting. She goes to take Aisha and Stella, so they can help the selkies, leaving Flora, Tecna and Musa to fight the monster. As they come, the selkies gets hurt. While the Winx were distracted, Tritannus attempts to escape.
Back at the cave, the others are doing their best to fight the monster. But as they surround it while Tecna is using her shield, Flora bounds the monster with her vines and Musa sends it away with her sound powers. Aisha captures Tritannus by using her Morphix to wrap him. Tritannus fights back, but Bloom and Aisha attacks too and Tritannus is stuck in middle of rocks and wrapped in Morphix. Bloom uses the opportunity and tells Tritannus to reveal Daphne's location, but Serena interrupts, telling that the lake is almost completely dry. The others ask Bloom to help, but Bloom still wants Daphne's location from Tritannus. Tritannus grins, saying "Go Fairy, save the pretty lake". Angered, Bloom tells him that its not over yet and flees with the others. Tritannus frees himself and shouts that it is over for now and swims back to Andros through portal.
There, the Trix are already waiting for his returm. Tritannus tells Icy that he has gift for her, drains Daphne's Sirenix powers and gives it to the Trix. The corrupted Sirenix power surrounds the Trix and Tritannus tells them that they are invincible as they have transformed into their Dark Sirenix.
Back at the Lake, the Winx use Harmonix Convergence to restore the Source of Sirenix with the selkies' and the fishes' help. As the source is restored, its water rises back again. The Sirenix Boxes appears with the Winx's Guardians of Sirenix and they form a circle around the Source of Sirenix. They use the powers given by the Winx's complete Sirenix Boxes to open a portal to the Infinite Ocean and disappear along with their Sirenix Boxes. The Supreme Guardian of Sirenix, Omnia, appears before the Winx and the Selkies, telling them that they are now Sirenix fairies and that they can enter the Infinite Ocean. The Winx are relieved and joyful upon completing the quest of Sirenix.
The Winx enter, transforming into Sirenix fairies. Once inside the Infinite Ocean, they admire their Sirenix transformation and their new hair color. Omnia then tells the Winx that thanks to their Sirenix powers, the Infinite Ocean is open to them forever. They go around the new world and Flora discovers some fishes that do not exist anywhere else. Omnia then reveals that each of them is granted a wish and that they can ask their guardians to grant it, but only after they have pleased destiny by defeating Tritannus. She also tells them that something evil has entered the ocean and Bloom immediately suggests Tritannus. Omnia adds that he is accompanied by others who possess Dark Sirenix and Stella suggests the Trix. Omnia tells them that in order to drive them away, they must fully develop their Sirenix, which Aisha promises they will work hard on while Bloom says that they will be beat Tritannus.
Finally possessing powers of all the selkies, Tritannus opens the Ocean Gate of the Infinite Ocean and enters it with the Trix, Daphne, and the mutants. Icy is excited that Tritannus fulfilled his promise of taking them there. Tritannus tells them that they can enter any ocean in Magic Dimension from there and conquer them. Daphne tells Tritannus that the Winx will stop him to which Tritannus disagrees and spears the green crystal near him. As pollution starts surrounding it, more and more mutants gather around it to bow down to Tritannus, who then tells that he will destroy the Winx.
- The Winx open the gate of the Infinite Ocean and gain Sirenix.
- The Trix receive a more evil and darker version of Sirenix called Dark Sirenix.
- Tritannus summons more mutants than ever.
- Daphne's Sirenix powers are absorbed by Tritannus and given to the Trix.
- Omnia (2D & 3D)
- Sirenix (3D)
- Dark Sirenix (2D & 3D)
- Bloom's Guardian of Sirenix
- Aisha's Guardian of Sirenix
- Daphne (3D)
- Trix (3D)
- Tritannus (3D)
- Mutants (3D)
- Selkies (3D)
- Winx Club
- Guardians of Sirenix
- Selkie Convergence - Used by the Selkies against Tritannus.
- Dragon's Embrace - Used by Bloom to defend the Winx but failed.
- Diapason - Used by Musa against the oil monster.
- Wove-Electronic Wall - Used by Tecna to block the oil monster's attack.
- Green Growth - Used by Flora against the mud monster.
- Reverberating Notes - Used by Musa against the oil monster.
- Mystic Wrap - Used by Aisha against Tritannus.
- Fire Blade - Used by Bloom against Tritannus.
- Power Swirl - Used by Aisha against Tritannus.
- Harmonix Convergence - Used by the Winx to restore the source of Sirenix.
- The simulator room appears for the first time since Season 2.
- This is the first time the Trix, Tritannus, and the Winx Club are shown in 3D in the TV series.
- This is the last appearance of Harmonix and the last hearing of the Harmonix song.
- This is the first hearing of the Sirenix song.
- This is the first appearance of the Winx Club and the Trix in their Sirenix forms in 3D.
- Starting with this episode, there is a new opening sequence. This new one uses three-dimensional computer generated imagery instead of two-dimensional hand-drawn animation and includes scenes of the 3D Sirenix transformation, the Winx Club in the Infinite Ocean and the official Season 5 trailer.
- This also lead toward a new section into this episode. CGI Art Director is Vincenzo Nisco.
- This also marks for all of the Winx's Sirenix Guardian shown in this episode as a group.
- The alternative title for this episode was "Crossing the Sirenix Gate".
- When the Selkies come together, Serena is not shown. A few moments later, she suddenly appears.
- During the fight with mud monster, when Flora performs her spell, her hairstyle is changed to her civilian's.
“Man, there's always a catch!”