The action of the series, just like in H2O - just a drop, takes place in the city of Gold Coast in Australia.
15-year-old Zac and his friend Cam are going camping on Mako. The island is supervised by sirens. The day of camping is a full moon day - accidentally Zac falls into the lake through a secret passage. Three sirens - Lyla, Nixie and Sirena help him. The next day, he discovers that he can control water and becomes the equivalent of triton. This situation causes all kinds of trouble for the mermaids the boy comes into contact with. They themselves are mermaids from birth and can only live in water. With the help of the moon ring, they manage to get the legs. With each step they get used to the land and learn to walk and behave like a normal person. But for everything to be all right, the mermaids must take his powers from Zac before they become more powerful.
