Barbie and Teresa tell us the fairy tale story of Liana and Alexa, best friends who share everything including their love of music. One day their simple lives change when they are given an enchanted mirror and befriend the girl trapped inside! To save their new friend, Liana and Alexa embark on a dangerous journey to the hidden Diamond Castle that will put their friendship to the test. But through the power of song and with the companionship of two adorable puppies, the girls face their challenges together and learn that friendship is the true treasure.