A mermaid from the Joseon period ends up in present-day Seoul, where she crosses paths with a swindler who may have ties to someone from her past.

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.

Shim Cheong (Jun Ji Hyun) is a mermaid who follows her one true love, a nobleman's son named Kim Moon from the Joseon Dynasty, to modern-day Seoul. Moon's modern doppelganger is Heo Joon Jae (Lee Min Ho), a highly skilled scam artist who first becomes interested in Shim Cheong because of a jade bracelet worth $6 million that Shim Cheong wears. With nowhere to go, Shim Cheong is taken in by Joon Jae, who also finds his con partners, Jo Nam Doo (Lee Hee Joon) and Tae Oh (Shin Won Ho), hiding out in his home from a vengeful past victim of their scams. Shim Cheong discovers a rival for Joon Jae's heart in Cha Shi Ah (Shin Hye Sun), a researcher at KAIST who deals with ancient artifacts. When a dangerous killer named Ma Dae Young (Sung Dong Il) sent by Joon Jae's stepmother who wants to make her own son the heir to Joon Jae's fortunes, can Shim Cheong survive her strange new environment while also helping Joon Jae avoid the dangers that await him?

In 1598, there is a county magistrate named Kim Dam Ryeong, in She County, Gangwon-do. He stayed at Yang's house by the seaside, and Yang took him to watch the mermaid he caught. Dam Ryeong asked Yang what he was going to do to catch the mermaid. Yang said that the fish oil extracted from the mermaid was of good quality and would not spoil even after being left for many years, and even the whale oil is hardly comparable to this grease, because of the nature of being rancid after a long time. Dam Ryeong pitied for this mermaid and took it back from Yang, and released it into the sea. In 2016, just as human beings would encounter traffic accidents even if they are unwilling, the mermaid comes to the land after the accident, and meets the first human being, Heo Joon Jae. After returning to the sea, the mermaid misses that man deeply. In order to keep the promise to meet the man again, she returns to land again and comes to Seoul. In the world of mermaids, she is the most arrogant and brilliant and clever, but in the human world, in the eyes of Joon Jae, she is just an idiot who eats a lot. This ignorant woman knows almost nothing about the world, and she believes what Joon Jae said firmly, and even learns the world through him. Unconsciously, he begins to feel guilty of lying to this woman. These two people who couldn't have coexisted, start a love story full of pathos.

Inspired by a classic Joseon legend from Korea's first collection of unofficial historical tales, about a fisherman who captures and releases a mermaid, this drama tells the love story between the son of a noble family in Joseon era and a mermaid. How can a mermaid from the Joseon era survive in modern-day Seoul? Shim Chung (Jun Ji Hyun) is a mermaid who finds herself transplanted to modern times. She is caught by Heo Joon Jae (Lee Min Ho), a charming but cold con artist who is the doppelgänger for Kim Moon, the son of a nobleman from the Joseon Dynasty. But in the present time, Joon Jae works with Jo Nam Doo (Lee Hee Joon), a skilled conman who guides Joon Jae to become a genius scammer. But Joon Jae's friend, Cha Shi Ah (Shin Hye Sun), who works as a researcher at KAIST, may be Chung's only hope for surviving in her strange new world.—KoreanDrama.org