Barbie and the Diamond Castle

Barbie and Teresa are playing music and writing a song together in the present. Stacie storms in after a fight with Courtney. Barbie and Teresa tell Stacie a story to teach her the power of friendship.

Liana and Alexa are two friends who love music and live in a cottage. They find two heart shaped stones and make them into necklaces to symbolize their friendship. The necklaces symbolize their bond as they continue to dream together.

A hungry moment leads Liana to share food with a poor woman who gives them a mirror in exchange. That evening, a voice speaks from the mirror and Melody emerges from within. The three girls bond over music and Melody teaches them a song.

The newly formed trio is soon attacked by a dragon named Slyder. They manage to escape, but their cottage is destroyed by the attack and burns down. The danger sets them on a new path away from home.

Melody explains she was once a pupil of the three Muses who lived in the Diamond Castle. Lydia turned evil and sought to take the castle for herself. The Muses were turned to stone and Melody was trapped inside the mirror.

Melody tells Liana and Alexa that Lydia can be defeated if they play the Muses' instruments. Liana volunteers to help, while Alexa reluctantly agrees to join the quest. The plan sets them on a journey toward the Diamond Castle.

On the way, the girls adopt two puppies named Sparkles and Lily. They are joined by twins Ian and Jeremy who offer their help and companionship. The group grows as they pursue the Diamond Castle.

Lydia tries to hypnotize the travelers with her flute, but the heartstone necklaces around Liana and Alexa keep the magic at bay. The group presses on, aided by the growing friendship and the protection of the stones.

The caravan reaches a grand mansion where the hosts, under Lydia's influence, declare themselves the prophesied owners. Alexa proposes staying, causing tension with Liana. Liana and Melody depart, while Alexa is captured by Lydia.

During their escape from the mansion, a magic bridge carries Liana and Alexa away, separating them from Melody and the twins. The separation heightens the stakes as they continue the journey in smaller groups.

Lydia creates a whirlpool and orders the girls to drown themselves; they pretend to be hypnotized to distract Lydia. Liana grabs Lydia's flute, and Melody shatters the mirror from inside it to stop Lydia. The mirror is swept into the whirlpool but saved by Sparkles and Lily.

Thinking the Diamond Castle can bring Melody back, the girls sing the song Melody taught them. The Diamond Castle reappears, and they step inside to find Melody freed from the mirror. They are rewarded with new dresses as they begin to reclaim their destiny.

The three of them play the Muses' instruments and sing together to overpower Lydia and Slyder, turning them to stone. The other Muses are freed, and Lydia's spells are undone. The girls are crowned princesses of music, and Melody becomes a Muse. The Muses give seeds to restore their garden and their old life returns to normal with a hopeful twist.

Barbie and Teresa return to the present, where Stacie goes to Courtney to apologize and make amends. The Diamond Castle life begins anew for Liana, Alexa, Melody, and their friends as gardens are restored and music flourishes.

Back in the present, the friends resume playing music together with renewed friendship and vigor, ending the tale with the power of song and companionship.