The familiar story of the earth-bound mortal falling for a mermaid is given a modern makeover. Lilly is a teenage mermaid who saves 15-year-old Spencer after he slides off his surfboard and nearly drowns in the sea. From then on, Lilly and Spencer tell their stories in alternating chapters. An underwater kiss leads both Spencer and Lilly to believe they have found their soul mate, with Lilly taking the initiative in the relationship, using a potion to sprout legs and go to high school.