Fearing Morgana and remembering Ursula, Ariel decides to withhold all knowledge of the sea world from Melody. The locket is tossed into the ocean, and a massive wall is built to separate the royal castle from the sea.
Twelve years later, Melody is still unaware of her mother’s mermaid heritage and is banned from ever going into the sea. However, she has been sneaking out the castle regularly to swim and one day finds her locket. Seeing her name on the locket, Melody confronts her mother in an explosive argument. Angry at her mother's refusal to answer her questions, Melody takes a boat and sails away from home. Her parents soon learn she is gone, and Triton uses his magic to transform Ariel back into a mermaid to search for Melody.
Melody is lured to Morgana’s lair by her manta rays, and Morgana uses the remains of Ursula's magic to temporarily transform Melody into a mermaid. Morgana says that the transformation will be permanent if she were to get hold of the trident, which she claims was stolen by Triton. With the help of Tip the penguin and Dash the walrus, Melody successfully returns to Morgana with the trident. Ariel tries to stop Melody, but before she can explain that Morgana is evil, Melody gives the trident to Morgana. With the trident in her grip, Morgana reveals her true intentions.
Morgana uses the trident's magic to lord over the ocean, rising to the surface to gloat. Scuttle, Triton, Sebastian, and Eric arrive, and a battle ensues against Morgana and her minions. Melody is able to grab the trident and throw it back to Triton by climbing up the cliff on which Morgana is standing and sneaking up on her. Triton uses his trident to encase Morgana in a block of ice, which sinks underwater.
Melody is reunited with her family, and Triton offers his granddaughter the option of becoming a mermaid permanently. Instead, she asks him to use the trident to disintegrate the wall separating her home from the sea.
*These tracks were originally recorded for the album Sebastian: Party Gras!.