Long ago, in a kingdom where music is outlawed, King Triton’s youngest daughter, Ariel, discovers her love for music in a secret, underground music club. Torn with the choice of whether to hide her passion or share it with her father and risk losing everything, Ariel sets off on a daring adventure to restore music to Atlantica.

A sixteen-year-old mermaid princess named Ariel is dissatisfied with underwater life and curious about human life on land. With her best friend Flounder, Ariel collects human artifacts and goes to the surface of the ocean to visit Scuttle the seagull, who offers very inaccurate knowledge of human culture. She ignores the warnings of her father King Triton, the ruler of Atlantica, and his adviser and court composer Sebastian that contact between merpeople and humans is forbidden.

Morgana, sister of Ursula, almost steals the baby Melody from her parents, Ariel and Eric. To protect Melody, she’s told never to enter the ocean, but by her 12th birthday, she’s been swimming there for years. She discovers the magic locket that was to be her christening gift, which makes her visible to Morgana. Morgana tempts her by offering her fondest wish, to turn her into a mermaid; however, to remain a mermaid, she’ll have to steal the magic trident from King Triton (who, unknown to her, is her grandfather). Meanwhile, all the sea creatures are searching for her. Along the way, she joins up with comic relief sidekicks Tip (a penguin) and Dash (a walrus). When she returns with the trident, Morgana’s evil nature is revealed, and there is a massive battle of good and evil.