Ariella is the crown princess of Meridia, a gilded underwater kingdom home to mermaids and mermen alike. For centuries her kind has preyed on unsuspecting humans, luring them from their boats and down into the abyss; on the eve of her coming of age ceremony, however, she feels an unexpected tug of compassion for a teenage boy being dragged into the waters. Risking the outrage of her father and the vengeance of a formidable sea witch, she rescues him and takes him to shore. Soon she is made to face the consequences of her decision and find out what life is really like above the surface.