The archenemies of the Winx Club, the Trix witches, team up with the evil nymph Politea and find out that, to defeat the fairies once and for all and become invincible, it takes very little: a Pearl hidden in the Deep of the Infinite Ocean! As small as powerful, the Pearl of the Depth gives enormous powers to those who possess it! For the Winx there is not a minute to waste: how will they stop the plans of their enemies before it's too late? Get ready: the most dangerous mission of the Winx is about to begin!

Sixteen years ago the most powerful warrior wizards of the Magic Dimension sacrificed themselves to fight against absolute evil. Now the fate of a kingdom is in the hands of a young girl - Bloom, the fairy of the Dragon's flame. Accompanied by her Winx Club girlfriends, Bloom must overcome the greatest challenge of all: enter the depths of the obscure dimension, fight against evil to bring her parents back to life and reveal the mystery linked to her origins. The destiny of the entire Magic Dimension depends on the outcome of this conflict.

Reunited with her birth parents, Oritel and Marion, Bloom discovers what it is like to live as a princess of Domino. Adding to her joy at being with her parents is the upcoming Princess Ball, which Sky has asked Bloom to attend with him. But Bloom's happiness is short lived when Sky is forbidden by his own father to escort her. Meanwhile, the evil Ancestral Witches who had once destroyed Domino join forces with the Trix - Icy, Darcy, and Stormy - to erase all positive magic from the Magic Dimension. To reverse the effects of the Witches' devastating reign of darkness, the Winx and the Specialists must travel to the cursed city of Avram and come face to face with the Trix and the Ancestral Witches. Only by defeating the witches can the Winx restore the positive magic in the entire dimension and regain their own powers.

Bloom is back home on her first school break, but the weird dreams she was having at Alfea have come with her. These dreams are trying to tell her something important.