Zac is a teenage boy who decides to camp on Mako Island, unaware that three mermaids, Sirena, Nixie and Lyla, who are guardians of the island, are watching him. That night, when the full moon rises, the boy comes into contact with the magic water of the Moon Pool. The following morning, Zac wakes up discovering he has become a merman with a fish-like tail and the ability to control and manipulate water. His new-found merman abilities will cause problems for the mermaids.　　The three mermaids, curious about living on land, are transformed into humans while in the moon pool during a full moon, now having the ability to live like humans.。看着他的背影消失，第五轻柔含笑的眼神突然变得疑惑，不解，喃喃道：“怎么会如此？如日中天之势已经形成，为何在这时刻天地逆转，对方竟然出现了一丝生机？”……