Plot

In the kingdom of Atlantica where music is forbidden, the youngest daughter of King Triton, named Ariel, discovers her love of an underground music club and sets off to a daring adventure to bring restoration of music back to Atlantica.

After a terrible tragedy in King Triton's once-happy undersea kingdom of Atlantica, the dejected ruler decrees that all music be banned from his realm. Almost a decade later, Princess Ariel--the most rebellious of Triton's seven charming daughters who still cannot understand why her father is against melody--sneaks out one night, only to discover an illegal speakeasy brimming with music. Excited, Ariel wants more; however, with a headstrong father and a vigilant nanny, she has her work cut out for her. Can Ariel, the little mermaid, restore happiness and harmony to Atlantica?—Nick Riganas

At least a year before the events of the original film, King Triton and Queen Athena reign over the underwater kingdom of Atlantica, a place filled with music and joy. They have seven young daughters: Attina, Alana, Adella, Aquata, Arista, Andrina, and their youngest, Ariel. One day, while relaxing in a tranquil lagoon above the surface, King Triton gifts Queen Athena a beautiful music box. However, their peaceful moment is shattered when a pirate ship approaches. As the menfolk flee, Athena attempts to retrieve the music box but is tragically killed when the ship crashes into the lagoon. Heartbroken by the loss of his wife, Triton throws the music box away and, in his grief, bans music from Atlantica forever.

Ten years later, Ariel and her sisters live under a rigid, monotonous routine imposed by their governess, Marina Del Rey, and her kind-heated assistant, Benjamin the manatee. Marina resents her role as the princesses' governess and dreams of becoming King Triton's attach, a position currently held by Sebastian the crab. Ariel, frustrated with her stifling life, frequently clashes with her father, creating a growing rift between them.

One day, Ariel befriends Flounder, a lively young tropical fish, and follows him to an underground music club. There, she is overjoyed to rediscover the beauty of music and is astonished to see Sebastian performing with a secret band. Initially, the musicians fear Ariel will expose them, but when she shares her memories of her mother and sings a heartfelt song, I Remember, they realize her sincerity. Moved by the joy music once brought to her family, Ariel swears to keep their secret and becomes part of the club.

When Ariel's sisters confront her about her recent absences, she reveals the club's existence. Excited by the prospect of music, they join her the following night and revel in the lively atmosphere. Unbeknownst to them, Marina secretly follows and discovers the club. Eager to secure her promotion, Marina reports its existence to King Triton. Outraged, Triton shuts down the club, imprisons Sebastian, Flounder, and the band, and confines Ariel and her sisters to the palace. He also appoints Marina to Sebastian's former position.

Heartbroken by the absence of music, Ariel decides to leave Atlantica. She frees her friends from the palace dungeon, and, despite initial reluctance, Sebastian leads them to a secluded place far from the kingdom. There, Ariel discovers her mother's music box, which Sebastian had hoped would remind her of happier times. Realizing her father has forgotten how to experience joy since Athena's death, Ariel resolves to return the music box to him. Meanwhile, Attina informs Triton of Ariel's disappearance, and the king orders a search. Determined to maintain her newfound authority, Marina sends her electric eels to hunt and kill Ariel and Sebastian.

As Ariel and her friends make their way back to Atlantica, they are attacked by the eels. Flounder bravely defeats them, but Marina confronts the group, leading to a battle with Sebastian. Although Sebastian traps Marina in a coral tube, she breaks free and charges toward him. Ariel notices Marina's attack and sacrifices herself to shield Sebastian, rendering herself unconscious just as King Triton arrives. Holding Ariel in his arms, Triton is overcome with guilt and sorrow. When the music box plays its melody, he sings to Ariel, and she awakens. The two reconcile, and Triton apologizes for his actions.

Moved by the healing power of music, Triton lifts the ban, restoring joy to Atlantica. Sebastian is reinstated as the king's advisor and named Atlantica's first official Court Composer. Marina and Benjamin are imprisoned for their crimes, and the kingdom celebrates the return of music. Ariel and Triton share a heartfelt dance, symbolizing their renewed bond and the happiness music has brought back to their lives.