While the Winx search for the Gem of Empathy, Tritannus breaks into Neptune's palace and turns everyone into mutants and Winx-hating monsters.
The annual mixer party with Alfea and Red Fountain takes place in Alfea's courtyard. All of the Winx, except Tecna, are there. Tecna was in her dorm talking with Timmy, until the Sirenix Book activates. Tecna opens it expecting another clue. It does, but rather than being written, it was in the form of music. Tecna quickly records it to play the song for Musa.
At the party, Bloom and Sky dance, the latter happy that he at least retrieved some of his memory back. He admits that he still may have forgotten how to dance, which Bloom was happy to help him remember. Kiko also helps out by imitating some dance moves for Sky to copy. When Sky was about to say something Kiko trips and so does Sky.
The girls are enjoying the party, all except for Aisha, who was still saddened about Nabu. Stella attempts to lighten her spirits by introducing three Specialists to her. Aisha was not in the mood and left with a huff, talking to them meanly. Musa comes out to find Riven listening to Kelli playing guitar, making her jealous. Riven follows her trying to explain things, but stopped when Musa stopped after hearing the musical message Tecna recorded from the Sirenix Book. It awakened memories of Musa's mother as it was revealed the music was a melody her mother once sung to her. The next clue is hidden somewhere on Melody.
In the dorm, Musa recalls the lyrics to the song about a ruby reef, and coral strings. She suggests that they go to her summer home on Melody where her mother first sang it to her. Stella and Aisha go to accompany her while Bloom, Flora, and Tecna remain at Alfea. They have now only got ten more days to find the Gems.
Meanwhile, Tritannus is lurking the oceans of Andros. He chats with Icy that he's preparing to meet his father for a little "family reunion". Icy sweet-talks him, saying she would like to be by his side to see that happen, much to Darcy and Stormy's disgust. Tritannus tells them to go find Daphne.
At Neptune's palace, King Neptune gets word of the fates of Ligea and Nereus. He vows to kill Tritannus for his treachery, but Tritannus arrives with his mutated servants. The palace guards rush him, but they were no match and were soon mutated by Tritannus. The fallen prince soundly defeats Neptune before also mutating him to be his servant. Tressa soon followed. Now Tritannus has mutated his entire family. All that is left is Aisha. Before leaving, he absorbs the power from Neptune's sword. He then heads for the gate leading to Melody's oceans. Sonna, the gatekeeper of Melody, tries to stop him, but she was overwhelmed and drained of her power. Tritannus passes through the gate and into Melody, as Sonna managed to sneak after him.
Stella, Musa, and Aisha arrive on Melody to head for Musa's summer home. As Musa reminisces about her home, much friction is going on between Stella and Aisha as Aisha was still pretty sour at Stella because of the incident at the party. Arriving at Musa's summer home, Musa remembers her mother as the beach house held a special memory of her. She suggests going into the water from there to find out the next clue, so they transform to Harmonix.
Before they could advance, Tritannus appeared before them. He fires a transformation beam at Aisha, but she gets shoved out of the way by Musa, who turned into a monstrous mutant seal. Stella and Aisha were forced to try and get away from the mutated Musa in the water. It was not made any easier as they tried hard not to seriously injure their friend. The two fairies rendezvous with Lemmy and Illiris, who tell the girls that there is a chance to revert Musa if they could find Sonna. Aisha and Lemmy go to search for Sonna while Stella and Illiris try to lure Mutant Musa to the gate. They succeed in getting Mutant Musa to encounter a weakened Sonna, who tries to calm her down. Slowly, Musa reverts back to her real self after she bonded with Sonna, who then recovered her lost power. Stella and Aisha were relieved that Musa has been restored. Stella and Aisha also patch things up between them.
The three find the Ruby Reef then remember the next part of the musical riddle. Musa seeks help from her Sirenix Guardian, who tells her to think about what her mother taught her when she sang the song to her. Musa then figured out that there might be something in the coral resembling a string instrument. They fan out to find such a coral. Musa then discovered a coral formation shaped like a harp, calling over the others, they play the coral harp, activating the next part of the riddle in the Sirenix Book back at Alfea.
Back at Alfea, the girls try to figure out the next part of the riddle that would lead them to the Gem of Empathy. Bloom leaves to solve another riddle: the riddle of Sky's memories. She and Sky take a nightly stroll around Alfea, where they both find two halves of a shell known as the Destiny Stone. According to Bloom, when two people who find both halves that fit, they will be together.
Daphne watches the scene from a viewing orb. Suddenly, it was shot down by Icy, as she, Darcy, and Stormy had found her. To Daphne's horror, Tritannus was there as well. He demands to know the secrets of Sirenix before shooting her with his trident. Bloom suddenly gets a headache as she sensed something horrible has happened...
- Neptune and Tressa get mutated by Tritannus.
- Only ten days remain until the lunar cycle ends.
- Tritannus turns musa into a monster
- Daphne is captured.
- Musa bonds with her Selkie, Sonna.
- Winx Club
- Alfea Staff
- Alfea Students
- Red Fountain Staff
- Red Fountain Students
- Dazzling Spiral - Used by Stella against monster Musa.
- Sun Boomerang - Used by Stella against monster Musa.
- Shining Mirror - Used by Stella to defend herself.
- This is the first episode of Season 5 to air in Italy before the US.
- This is the fourth time the Winx had to fight against another Winx Club member. First was against Dark Bloom, second against Aisha, third against Tecna, and fourth against Musa.
- The alternative title for this episode was "The Sirenix Song".
- During the scene when Tecna was in the her room, she had a highlight in her hair even though she wasn't at the party when Stella gave the Winx hair hightlights.
- In one scene, Sky's gem is orange instead of blue. And in another scene, it is green.
- When Aisha walks off after splashing a drink on Miles, he can be seen in the background even though he was just next to Aisha.
“You guys need to cool off!”
“Ugh! I'll be thinking about you.”
“Phylla will return! Phylla will defeat you!”
“You may not enter the gates of Melody, monster!”
“We would have knocked, but there's no door.”
“Who lives under a lake?”