The Winx go to Andros, Aisha's home planet, to participate in the festival of the kingdom. an old friend of the Winx, queen Ligea, attends the festival as well. Meanwhile, Obscurum and the staryummies attack Gorgol, the underwater star of Andros. The Winx, aided by Nex, decides to go on a new underwater mission to save Gorgol, and to do so, they use their old power, Sirenix, and dive into the ocean of Andros. Underwater, they face the Hunter of the Seas, a predatory monster sent by Valtor. They manage to defeat it by trapping it in a cave with no way out.