Rebellious 15 year old mermaid, Mirabel Madrigal, is fascinated with life on land. On one of her visits to the surface, which are forbidden by her controlling father, Ballister Boldheart, she falls for a human prince. Determined to be with her true love, Mirabel makes a dangerous deal with the sea witch Lord Dominator to become human for three days. When plans go awry for these two love birds, Ballister must make the ultimate sacrifice for his daughter.