A big wave grabs a ballerina music box during a thunderstorm, and Ariel, Flounder, and Sebastian tried to get it, but it was unable to reach. Ariel befriends a deaf mermaid, and both of them decide to seek out the magical Wishing Starfish to make their dreams come true.
During one of her raids for human things on the surface, Ariel stumbles upon a musical ballerina. Enchanted by the ballerina (both the trinket and the real thing), Ariel suddenly wants nothing more in the world than to be able to dance the ballet, but she realizes she lacks the "two tails" required to perform the dance properly.
As she laments her desire to dance, she meets Gabriella and Ollie, a pair of best friends not that unlike Ariel and Flounder. Ariel tells Gabriella of her dream to dance with two tails, and Gabriella responds that she, too, has a dream, and hers is to be able to sing. Ollie then tells them about the Magical Starfish who is said to be able to grant them a wish should they be able to brave Killer Crab Canyon and the Cave of Terror to get to the other side.
Ariel, of course, wants to go, and drags Sebastian and Flounder with her. Along the way (and between avoiding various dangers including a moment where Sebastian distracts the Killer Crabs by talking non-stop), Ariel and Gabriella bond in their alarming similarity of adventurousness. Soon enough they reach their destination, and make their wishes to the Magical Starfish.
However, it turns out the Starfish isn't as magical as advertised, and cannot grant them their wishes. Though they are sad, Ariel realizes that what they really wanted in the end was to be able to express their inner feelings, which they thought they could only do through dancing ballet (in Ariel's case) and singing (in Gabriella's case).
By the end of the episode Ariel is quick to realize that Gabriella never really lacked anything in the first place, despite not having a voice, and they celebrate what they already have in Daring to Dance.
- This is the first appearance of Gabriella.
- The title is a play on "When You Wish Upon a Star" from the animated film Pinocchio.