Niall Horan, a band member of One Direction, doesn't have just one secret. He has two. 1.) He has a younger sister named Isabella. 2.) He is a merman, and Isabella is a mermaid. When Niall was nine, and Isabella was eight, they found an island named Mako Island. It was a full moon, when they finished exploring, they jumped into a pool of water and they became half fish, and received powers. Tattoos were burnt into their skin at the back of their neck. A tattoo of a seashell. They were also given shark tooth necklaces. The shark tooth necklace is important. If they want to get into water without turning into a mermaid, and a merman, they have to wear them. It's a lot harder when Niall's bandmates don't know about his secrets. But, what happens when a scientist wants to find out what, or who, Niall and Isabella, really are.