Alima is siren appointed by her queen to go up to the human world. Her mission: to find the lost princess who has mysteriously disappeared without a trace. Although she hoped that she'd complete the mission without exposing her secret, she meets Freddy, a nineteen year-old fisherman who finds out her secret instantly. The two quickly become friends and together, they are determined to find the princess.
Along the way, they meet several other mermaids from around the world, all appointed by the queen, all after a prize given to the first mermaid who finds the lost princess. The competition is fierce, every mermaid is for herself. But all face the same threat: the scientists. Though each girl has their eyes on the prize, they must face the fact that in order to find the lost princess and prevent the scientists from discovering their secret, they will have to work together, whether they like it or not.
They all wonder the same questions: "Who will get the prize? How could they hide their secrets? And lastly, where is the Princess?"