So how does a Joseon-period mermaid make it through contemporary Seoul? Shim Chung is a mermaid who has been stranded in the 21st century for whatever reason. His doppelgänger Kim Moon's son, Heo Joon Jae, a charming but icy con artist from the Joseon Dynasty, catches her. Despite this, Joon Jae is working with Jo Nam Doo, a conman who has helped Joon Jae become a master scammer in the modern era. But Cha Shi Ah, a researcher at KAIST, may be Chung's only shot for survival in this weird new world that Joon Jae's friend has brought her into.