Lovesick over the prince, the mermaid learns from her grandmother about the fate of mermaids and how marriage to a human can give a mermaid an immortal soul. Thus, while still wearing her crown and oysters, she seeks out the sea witch wearing her powerful necklace who will give her a pair of human legs in exchange for her voice and intense pain while walking. However, if the prince falls in love and marries someone else, the mermaid will turn to seafoam. Will the mermaid take this deal? Will she try to barter something else? And will the spell succeed?

Before that, however, they will need the following ingredients to gather the potion: red seaweed, blue shrimp, yellow clams, and a purple starfish. All of these items can be found within the sea witch's cave, but they are protected by a spell that will repel them. They must sing a song involving the item in question to dispel it and gather the item. Then they must come up and sing a duet about the potion while making it.