Graduate student Leo arrives at Merfolk Island and mistakes the powerful siren Opal for a merman. Teaching him courtship songs, Leo unknowingly makes Opal believe he loves him. Opal has waited over a decade for Leo, who once rescued him but lost his memory. When Leo learns the truth, he flees, only to be imprisoned by a heartbroken Opal. Amid misunderstandings and passion, they reconcile. Leo proposes with their unborn child, and Opal gains legal status. They marry and welcome their baby siren.