How can a mermaid from the Joseon era survive in today’s modern Seoul? Shim Chung (Jun Ji Hyun) is a mermaid who finds herself catapulted into the modern era. She is captured by Heo Joon Jae (Lee Min Ho), a charming but cold-hearted con artist who bears a striking resemblance to Kim Moon, the son of a Joseon-dynasty nobleman. But in the present day, Joon Jae works with Jo Nam Doo (Lee Hee Joon), a seasoned con artist who wants to turn Joon Jae into a master con artist. The mermaid’s only hope for survival in this strange new world may lie with Joon Jae’s friend, Cha Shi Ah (Shin Hye Sun), who works as a researcher at KAIST.