Once upon a time, a Joseon-era mermaid finds herself transplanted to modern-day Seoul. She is caught by Joon Jae, a genius swindler who looks exactly the same as Kim Moon, the son of a nobleman from the Joseon Dynasty. In present time however, Joon Jae is a skilled conman on his way to become a genius scammer. His friend, Shi Ah, is a researcher at KAIST, and may be the mermaid’s only hope for survival in this strange new world. Will she get her happily ever after?