H20 takes place on the sunny coast; surf, sand and never-ending sunshine. Here we meet Emma, champion swimmer, her friend Cleo and rebellious new girl Rikki. When bad boy Zane plays a prank on Cleo, the three girls find themselves stranded on Mako Island. There, they discover a secret pool where, by the magical powers of the full moon, they are turned into mermaids! Any contact with water makes them sprout a tail in ten seconds – but once they dry off, they return to human form. They also now have strange powers over water which Cleo uses to get even with Zane. Can the girls be normal teenagers with this crazy secret?