When Mia returns to her old family summer home for the first time since her parents' death, she is suddenly taken back into the unicorn world of Centopia through the magical portal. There she meets Iko, an elf from Lotus Island, who desperately needs her help. Toxor, a monstrous, toad-like, vindictive villain, is taking over Lotus Island, transforming its fabulous citizens into an army of will-less henchmen with its dark magic. Mia, and her old and new friends, must band together to follow in the footsteps of the mythical heroine of Centopia and unite three ancient, magical power stones to defeat Toxor. When faced with the biggest villain Centopia has ever known, Mia will learn what it really means to be a hero, and that true strength lies not in the power to defeat an enemy, but in the courage to treat an enemy in need, as a friend.