The young mermaid princess Sereia hears from her sisters about the wonderful life that humans lead on the surface and about the enchanting human prince Lucas, whom she promptly saves from drowning. Sereia is immediately smitten and turns to the sea witch Revina, who makes a pact with her: For one year, Sereia will take on human form and may try to win Lucas' heart. But the price is that she will lose her voice in the human world and be banished if she fails to win Lucas over. Together with her good friend, the sea turtle Sheldon, Sereia takes the risk and leaves the safety of the underwater world.