King Triton, the ruler of the underwater kingdom of Atlantis, is devastated when his wife, Athena, is killed during a pirate attack while attempting to retrieve a music box he had presented to her. Thusly, he bans all music from the kingdom.
Ten years later, Triton's seven daughters, the youngest being Ariel, live under a strict routine maintained by their governess, Marina Del Ray, and her assistant, Benjamin. Marina is unsatisfied with her role as the girl's governess and longs to be Triton's attaché, a role currently filled by Sebastian the crab. Ariel, who longs for music to be returned to the kingdom, follows a fish named Flounder to an underground music club, where she discovers Sebastian illegally performing. The music performers initially believe Ariel will expose them to Triton, but she joins the club with an oath.
Ariel reveals the music club to her sisters, and the following night, they arrive to join the music performers. However, Marina reports their activities to Triton, who imprisons Sebastian, Flounder, and the band, while Marina becomes Triton's attaché.
Ariel, after an argument with her father, frees the imprisoned band. They arrive at a deserted area where they discover the music box, and Ariel decides to return it to Triton, hoping it will change his mind. In the kingdom, Ariel's eldest sister Attina alerts Triton and Marina to her disappearance. Marina decides to kill Sebastian and Ariel, and takes a group of eels to attack the band. In the ensuing confrontation, the band manages to defeat the eels by the time Triton arrives. However, Marina makes a final attempt to kill Sebastian, but Ariel intercepts and is knocked unconscious instead. A remorseful Triton sings the lyrics of Athena's song, awakening Ariel. Triton apologizes for his actions and takes the band back to the kingdom, ordering Marina arrested as well.
Triton allows music to be returned to the kingdom, and appoints Sebastian as the kingdom's new court composer, much to the kingdom's rejoice. Meanwhile, Benjamin concedes with an imprisoned Marina and convinces her to give up her evil ways.
- Jodi Benson as Ariel.
- Samuel E. Wright as Sebastian.
- Jim Cummings as King Triton.
- Sally Field as Marina Del Ray.
- Parker Goris as Flounder.
- Tara Strong as Adella/Andrina.
- Jennifer Hale as Alana.
- Grey Griffin as Aquata/Arista.
- Jeff Bennett as Benjamin.
- Kari Wahlgren as Attina.
- Lorelei Hill Butters as Queen Athena.