It follows the story of Liana and Alexa (the in-universe roles of the dolls, Barbie and Teresa)[4] on their journey to find the mysterious diamond castle.

The trio bond over music and Melody teaches them a song; but they are soon attacked by a dragon named Slyder.

Melody explains that she was once the apprentice of the three Muses, Dori, Phaedra, and Lydia, who lived in the Diamond Castle.

When they refuse, Lydia attempts to hypnotize them with her flute but they are shielded by the stones on their necklaces (revealed to be from the Diamond Castle).

The girls escape with the help of twins Ian and Jeremy who join them on their journey; but are separated when Liana and Alexa are carried off by a magic bridge.

Liana and Melody leave and Alexa angrily takes off her necklace, whereupon she is captured and hypnotized by Lydia.

The three of them play the Muses' instruments and sing together, overpowering Lydia and turning her and Slyder to stone.

Melody invites them to live in the castle, but they choose instead to return to their old life with their new pets; the Muses give the two magic seeds which blossom instantly into golden flowers.

Back to the present, Stacie realizes nothing can break true friendship and goes to apologize to Courtney; Barbie and Teresa happily resume playing music.