When Mia discovers her stone is far more powerful than she ever knew, she accidentally activates an ancient prophecy and sends herself on a one-way trip to Centopia! Trapped in the magical unicorn realm, Mia partners with a mischievous and unlikely new friend and undertakes a perilous journey to face the monstrous villain, Toxor, who possesses the only thing that can send her home. But Toxor seeks an evil dominion over all of Centopia, and when Mia learns the cost of returning home will darken the fate of the entire unicorn world, she must make a difficult choice. Will Mia forgo her human existence to stay and protect the enchanted world she loves, or return to her life in the human world and leave Centopia behind, forever?