Civil war breaks out in the mermaid kingdom. To protect Princess Chu Yunling, who bears a crucial mission, the mermaid queen seals her spiritual power and sends her to the mortal world.
Four royal mermaid guards set out to find Chu Yunling and uncover the truth behind the turmoil. They descend to the human world separately and disguise themselves as a doctor, a superstar, a CEO and a mafia leader respectively. Then they start an extraordinary journey together with Chu Yunling, who now lives as a mortal girl named Xia Shiyue...
