A long time ago, there was a young mermaid named Buttercup. She was beautiful and had a lovely singing voice. However, she wasn't like other mertoons; she was in love with land-life. One day, she confronts Chrystalis the sea witch, who, in exchange for Buttercup's voice, turns Buttercup into a human. Another tie in: the prince she wants to be with has to kiss her by the sunset of the third day, otherwise she turns back into a mermaid and is Chrystalis's slave. When she turns human, she meets Prince Butch, a kind, handsome young man, and they instantly fall in love. However, she is later betrayed by Chrystalis, who turns herself into a beautiful girl using Buttercup's voice. She now has to stop Butch and Chrystalis's wedding before the third sunset. Will she be able to remain human? Well...