The series tells the story of three girls - Emma, Cleo and Rikki, and later Charlotte and Bella, who accidentally discover a magic cave and learn the ability to turn into a mermaid in 10 seconds after each contact with water. Since then, their lives have become very complicated. They want to keep their secret a secret, but they do not always succeed. The girls are helped by a few trusted guys like Lewis and Will. They must also be careful during a full moon, as the operation of the moon is dangerous for them. The action of all episodes takes place in the city of Gold Coast in Australia.
