Inspired by a classic Joseon legend from Korea's first collection of unofficial historical tales, about a fisherman who captured and kidnapped a mermaid, this drama tells the love story between the son of a Joseon noble family named Kim Dam Ryung (Lee Min Ho) and a mermaid he named Se Hwa (Jun Ji Hyun). Sometime during August, 1598, newly appointed governor Kim Dam Ryung stays for a night at an inn run by Lord Yang (Sung Dong Il). During that evening, Lord Yang shows Dam Ryung a captured mermaid named Se Hwa. Later that night, Dam Ryung releases her into the ocean and, before she swims away, Se Hwa reaches out her hand to Dam Ryung which he briefly holds. In the present day, Heo Joon Jae is a smooth talking conman with magician like abilities. He works with Jo Nam Doo and Tae Oh. For their next score, Joon Jae impersonates a prosecutor and swindles a large amount of money from a wealthy suspect's mother. Joon Jae then escapes to Spain and stays at an oceanside resort. Meanwhile, Shim Chung is a mermaid who gets caught in a tidal wave and is washed ashore near the oceanside resort. There she meets Joon Jae.