The film continues the story of Ariel (Halle Bailey) and Prince Eric (Jonah Hauer) as they face new challenges to maintain peace between the human world and the ocean. After becoming part of the land, Ariel has been living happily with Eric and their young daughter, Melody.

However, everything changes when an ancient threat from the deep sea resurfaces, endangering both worlds.Melody, curious about her oceanic heritage, accidentally embarks on a dangerous adventure when a new villain—Morgana, Ursula’s sister—emerges with a plan for revenge. Ariel is forced to return to the ocean, confronting old memories and new dangers to protect her daughter and the future of the aquatic world.