Season 1
How can a mermaid from the Joseon era survive in modern society? Sim Chung is a mermaid who follows her one true love, a nobleman’s son named Kim Dam-Ryung from the Joseon Dynasty, to modern-day Seoul. Dam-Ryung’s modern doppelgänger is Heo Joon-Jae, a highly skilled scam artist who first becomes interested in Sim Chung because of a jade bracelet worth $6 million that Sim Chung wears. With nowhere to go, Sim Chung is taken in by Joon-Jae, who also finds his con partners, Jo Nam-Doo and Tae-O, hiding out in his home from a vengeful past victim of their scams. Sim Chung discovers a rival for Joon-Jae’s heart in Cha Si-A, a researcher at KAIST who deals with ancient artifacts. When a dangerous killer named Ma Dae-Young, sent by Joon-Jae’s stepmother who wants to make her own son the heir to Joon-Jae’s fortunes, can Sim Chung survive her strange new environment while also helping Joon-Jae avoid the dangers that await him?
Episode 1
In 1958, the nobleman Dam-Ryung releases a mermaid back into the ocean. In present-day Seoul, the figure of conman Joon-Jae stands on the same spot.
Episode 2
Joon-Jae brings a beautiful woman back to his hotel, unaware that she's a mermaid. Jin-Ok realizes she's been scammed and sends men after Joon-Jae.
Episode 3
With no memory, Joon-Jae finds himself alone on a beach next to a jade bracelet and a single pearl. Meanwhile, the mermaid crosses the ocean to Seoul.
Episode 4
At the aquarium, Joon-Jae runs into a woman being chased by security. Feeling a sense of déjà vu, Joon-Jae rescues her and brings her home.
Episode 5
Joon-Jae lives with the woman who he names Sim Chung. Fugitive Dae-Young has been on the run for 3 months when a murder occurs near Joon-Jae's house.
Episode 6
Sim Chung is involved in a traffic accident. Joon-Jae rushes to the hospital to find her in critical condition.
Episode 7
Joon-Jae tells Sim Chung he loves her. Meanwhile, detective Hong comes across Dae-Young while investigating a murder.
Episode 8
Jung-Hoon teaches Sim Chung that jealousy is the way to a man's heart. Meanwhile, Joon-Jae sees an image of a man with a mermaid on an ancient vase.
Episode 9
Joon-Jae finally faces off with his pursuer Dae-Young. He suffers a major injury and confesses his feelings to Sim Chung before losing consciousness.
Episode 10
In a museum, Joon-Jae sees a figure in a painting that looks just like him. Unable to identify the figure as Dam-Ryung, he grows distraught.
Episode 11
Sim Chung leaves the house after learning Joon-Jae is a conman. In a panic, Joon-Jae desperately searches for her.
Episode 12
Joon-Jae is arrested by detective Hong. When Sim Chung realizes they are in danger, she tracks them down.
Episode 13
Joon-Jae is still having strange dreams. Sim Chung hears Joon-Jae say the name Se-Hwa in his sleep. She asks him who he is talking about.
Episode 14
With Professor Jin's help, Joon-Jae learns he is an ancestor of Dam-Ryung. To avoid a tragic fate, he decides to protect Sim Chung whatever it takes.
Episode 15
Sim Chung's heart will stop without Joon-Jae's love. Upon learning this, Joon-Jae talks about his dreams and finding out that Sim Chung is a mermaid.
Episode 16
Joon-Jae and Yoo-Ran have an emotional reunion at Sim Chung's birthday party. Joon-Jae learns why Dae-Young has been chasing him.
Episode 17
After almost being caught by Dae-Young, Sim Chung erases his memory. In the process, she witnesses the final moments of Dam-Ryung and Se-Hwa.
Episode 18
After Il-Joong's death, detective Hong gets a warrant to search Seo-Hee for evidence. Meanwhile, Chi-Hyun threatens Nam-Doo to get him to cooperate.
Episode 19
Chi-Hyun points a gun at Joon-Jae, but Sim Chung jumps in front and is shot. She slips into a coma, causing Joon-Jae to fall into despair.
Final
Sim Chung erases Joon-Jae's memory and returns to the ocean. When Joon-Jae wakes up, there's only a single pearl next to him. Three years pass...