In the kingdom of Andros, Aisha's uncle Neptune plans to make his son Nereus a prince, Nereus's twin brother disrupts the crowning ceremony and is sent to prison.

The Winx change their concert, into a benefit to help clean up the oil spill. Meanwhile Tritannus escapes from jail with the help of the Trinx and begins absorbing the oil spill's pollution and slowly begins transforms into a monster.

The girls all head back to Alfea to talk more with Ms. F and read up o a book called The Sirenix. While in the library they are attacked by both the Trinx and Tritannus: who is getting stronger. Sky takes a hard blow to the head.

Krystal attempts to heal Sky's memory, but the memory of losing the pendant of Eraklyon is causing the blockage, but only Sky knows where it can be found. Timmy helps Tecna update her phone to find the Sirenix Book, which the Trix secretly sabotage. While, searching for the Sirenix Book, the Winx find the fake one, which turns Tecna into a terrifying robot, whose mission is to find the Sirenix Book.

The Trix show their powers, wondering if they are strong enough to go up against The Winx Club. As the Trix get stronger, so do the Winx.

In order to fix this new threat, the Winx must gain a new power, called 'Harmonix'. It not only gives them new outfit, but now they can fight in the air, land, and under water a lot easier.

Tritannus raids King Neptune’s underwater palace and transforms his whole mer family into mutants. Then, thanks to the dark magic of his trident, he manages to absorb all of the magical strength and energy of his father, King Neptune’s, mystical sword. Meanwhile, the Winx Club get a second clue to Sirenix which leads them to Musa's home world, Melody, busy searching for the second gem, the one of Empathy. During a fight with Tritannus, Musa is hit by a powerful dark spell and transforms into a terrible monster, bent on destroying the Winx. The Trix arrive with Tritannus on daphne`s doorstep and force her to tell them about Sirenix.

Continuing their quest to find all the mystical gems, Bloom, Aisha and Tecna go to Tecna's home world, Zenith, to find the second gem of empathy. Meanwhile, Musa, Flora and Brandon watch over Stella who has accidentally turned into a little kid! Will the Winx find the second gem, and turn Stella back to normal?

During a day of races that are taking place at Alfea with current, & past students of Red Fountain, the Trix attack and create lions out of dark magic to fight the Winx for them.

Bloom and some of her friends head to her home world for a celebration, along with Sky. However it is interrupted when the witches cause trouble underwater. Sky is left along with Blooms parents when the are attacked.

Both Bloom, and the rest of the Winx Club have gained the ability to cross the Gates, but the Witches have stolen Daphne's powers, and can now do do it too.

Bloom's plans to head home for Christmas are interupted by the Trix. They have trapped the girls at their old school with Ice dragons to keep them at bay.

After having a picnic on a dirty beach the Winx decide to clean it up, while Stella tries her hand at a fashion show. Meanwhile Tritannusgains more power, but looses his toxic one.

The Winx battle it out agents in Trix. Sirenix VS Sirenix.

As darkness envelopes the magical worlds, everyone looks to Stella to help save them and her father's life.

Daphne tries to warn Bloom of Tritannus' plans; Mike and Vanessa's attempt to clean up Garbage Island is interrupted by a monster attack.