Lena, a young and carefree mermaid princess, lives a happy life in her home under the sea until the day she meets a human, Prince Stefan, and falls desperately in love. Realizing that her only chance would be to become a human herself, Lena visits the wicked Cassandra, who in exchange for her lovely voice, gives her what she desires, warning the princess that if Stefan married someone else, she would then be turned into sea-foam for all time.