As Flounder, Sebastian, and Ariel are playing hide-and-seek, a cranky sorcerer blowfish swims into the area. When Sebastian accidentally grabs the sorcerer blowfish's tail by mistake, chaos ensues, in which Ariel typically bursts into a fit of laughter. Angered, the sorcerer blowfish casts a spell on her (unseen by Flounder and Sebastian) that would trigger devastating seaquakes every time she laughs. Sure enough, when she starts laughing at Sebastian's antics, a seaquake occurs. The sorcerer blowfish also warns her that if tries to tell anyone, the seaquakes would also happen.
A week passes by. Sebastian and Flounder have brought Ariel before King Triton, reporting to him that she hasn't been laughing. Sebastian tries to make her laugh, and sure enough Ariel completely refrains from even cracking a smile. She insists that nothing is wrong, and that she only wants to be more serious, and swims off. King Triton expresses his worry, and tells Sebastian and Flounder to cheer her up. They try again and again to make her laugh with their crazy antics, and when they finally succeed, a terrible seaquake hits Atlantica. Ariel decides that she has no choice but to leave, which she does, after giving a quick goodbye to Flounder and Sebastian.
Ariel starts searching for the sorcerer blowfish until a purple colossal squid tells her to go to Avlo-Kadavlo, a kingdom far away from Atlantica. Flounder and Sebastian, who have been following her secretly, are spotted by a pair of a blue and purple sorcerer blowfish, who take turns using their magic on them, eventually exchanging their bodies, so that Sebastian has Flounder's body, and vice versa.
Meanwhile, Ariel has found the orange sorcerer blowfish who cast the spell on her. Finding a twist in the curse, Ariel laughs at him, causing a seaquake to erupt all around them. Hence the orange sorcerer blowfish has no choice but to take the spell off her. Just then, Sebastian (in Flounder's body), and Flounder (in Sebastian's body) show up. Ariel convinces the orange blowfish to change them back, which he does. The pink and blue blowfish appear to tell them that it's against the law to take off another's spell, and send the group to work in the bubble mines.
Working in the bubble mines, Ariel tries to understand why the orange blowfish is so cranky. It seems that he feels his magic is inferior compared to the other blowfish. Ariel suggests that the other blowfish are more powerful because they enjoy what they do. With this thought in mind, the orange blowfish turns himself, Ariel, Sebastian and Flounder into a giant sea serpent and escape from the bubble mine. The blue and purple blowfish try to use their magic on them, but fail and swim away. Thus their disguise wears off and they laugh to their hearts' content.