Barbie returns in a brand-new musical fairy tale! Far away, in a land of music and magic, live two beautiful girls. Liana and Alexa are best friends who share everything-especially their love of singing. One day, while walking through the forest, the girls find a magical mirror. As they clean the mirror and sing, something amazing happens! A girl named Melody appears in the mirror's surface. Melody tells the girls about the secret of the Diamond Castle. The Diamond Castle, Melody explains, is the home of all music, where three musical muses once resided-until one evil muse, Lydia, tried to take the castle for herself.