After a run in with the local bad boy, best friends Cleo and  Emma, along with the new girl Rikki, find themselves accidentaly stranded on a mysterious island. After exploring the strange island, the friends try to swim to freedom through an eerie underwater channel. But as they try to escape, the full moon has a  magical effect on the water and changes the girls forever- turning them into mermaids! The girls just want to live normal lives but as they start to come to terms with their new tails, not to mention their magical powers over H2O, they start to realize that they may never be normal again.