In the year 1598, Kim Damryeong stayed at Mr. Yang's house. At the little pond, he met the mermaid's eyes. Damryeong felt sorry for the mermaid, so he sent the mermaid to the sea under the guise of Mr. Yang's crime. Hence, their long relationship started.

Heo Joonjae becomes soft-hearted after seeing the mermaid waiting for him, so he brings the mermaid to his house. The mermaid is addicted to the new world of Joonjae's laptop. Meanwhile, Joonjae and the mermaid become fugitive due to the chase of Jang Jinok.

Joonjae was left alone with a jade bracelet and a grain of pearl after falling from a cliff, he barely managed to arrive in Seoul and hurried in to resolve a fraud case of madam. Meanwhile, the mermaid begins a rough journey to Seoul to keep the promise.

Joonjae, who had never seen a mermaid before felt a strange sense of vision and helped her escape from the aquarium... On the other hand, a murder happened next door to Joonjae while the whereabouts of Ma Daeyoung is unknown for three months.

Joonjae falls in a panic state after seeing Cheong is bedridden at hospital emergency room. Heo Chihyeon receives investigation at the hospital. Meanwhile, Jo Namdoo finds a tape recorder that is attached to a black box inside of Chairman Heo Giljoong's car.

Having lost some memory, Joonjae is confused, Hong Dongpyo encounters Ma Daeyoung.

Cheong is annoyed by Yoo Jeonghoon's advice; Joonjae feels strange about Namdoo's loss of communication.

Joonjae is relieved to know that Cheong is with him; Joonjae discovers that the man who threatened him was an escaped prisoner.

Joonjae is troubled by Damryeong's identity; Joonjae and Namdoo receive an invitation from Ahn Jinjoo.

Cheong finds out that Joonjae is a swindler; Joonjae focuses on finding Cheong; Dongpyo finds out about Daeyoung's past.

Jinjoo decides to meet with Kang Seohee again; Joonjae is caught by Dongpyo.

Cha Shia and Mo Yooran visit Joonjae's house; Joonjae discovers something strange.

With the help of Professor Jin, Joonjae finds out that he is on the same path as his previous life, so he decides to protect Cheong.

After learning about Cheong's terminally ill heart, Joonjae cannot conceal his sadness.

Joonjae and Yooran have a talk; Namdoo questions Yooran; Chihyeon asks Seohee about his biological father.

When Cheong sees the end of her previous life with Joonjae, she becomes confused.

After Chairman Heo's death, Joonjae and Dongpyo speed up their investigation; Chihyeon approaches Namdoo.

Joonjae suffers from unexpected circumstances; Daeyoung visits Professor Jin in an attempt to regain his memory.

Before returning to the sea, Cheong says farewell to people; Joonjae does some embarrassing acts.