Cheon Sang-hyuk has been trapped on earth for 500 years and has lived as ‘Cupid’, a matchmaker of humans. Oh Baek-ryeon, an ethereal beauty who committed a great sin in her past life, is doomed to fail every romantic relationship in this lifetime. Just when she is about to give up in love, her fairy Cupid appears in front of her.

Baek-ryeon feels a weird sense of familiarity upon encountering Cheon Sang-hyuk. He secretly watches her wondering why she doesn’t have the red thread of fate unlike the other humans. Meanwhile, the night before the snowstorm, a woman gets kidnapped in a public parking lot in Mt. Inwang, and the witnesses of the incident are found dead one by one.

Baek-ryeon expects Sang-hyuk, who heroically saved her from her stalker, to be the man of her destiny, but he draws the line that he does not want to be in a relationship with a human. Meanwhile, Sang-hyuk and Jae-hee run into each other at Baek-ryeon’s animal hospital. How were they related to each other in their past lives?

500 years ago, Cheon Sang-hyuk, a fairy who had no ties to humans, ignored the warnings of Samsin and fell in love with a human girl. As a punishment, his wings got burnt off and he lost his beloved woman. 500 years later, since he well understands the pain of being alone, he empathizes with Baek-ryeon and eagers to help her out. So he starts by asking her what her ideal type is.

Sang-hyuk begins to suspect that the culprit in the Inwangsan missing girl case and the 1993 missing high school girl case are the same person. Baek-ryeon is upset because Sanghyuk tries to set her up with a random man while she has a crush on none other than Sanghyuk himself. At last, after climbing Mt. Inwang a thousand times, she gets to meet the man of destiny.

Sang-hyuk and Jae-hee learn that Baek-ryeon was a witness to the Inwangsan disappearance incident. In order to protect Baek-ryeon, Sang-hyuk chases down the criminal like her knight in shining armor. Baek-ryeon is happy when Sang-hyuk protects her like Superman and doesn't get hurt even after the intense physical fight, and she gets very curious about his true identity.

The disappearance of a high school girl in 1993 still remains unsolved as Sang-hyuk, who was in charge of the case, has disappeared from the human world for decades. Sang-hyuk is convinced that the culprit of the missing high school girl case and the culprit of the Inwang Mountain missing woman case are the same person, and he actively participates in the investigation.

Baek-ryeon goes to find the street she saw in her dream. Although it is her first time to see that street, she feels strangely familiar and her heart starts to ache. The more Sang-hyuk learns about his feelings for Baek-ryeon, the more he becomes afraid of approaching her. He doesn't believe he deserves her.

Sang-hyuk remembers Baek-ryeon saying she was an angel when she was drunk, and he secretly hopes that she actually is an angel. Meanwhile, Go Eun-seo, a missing woman from Mt. Inwang, calls Baek-ryeon and tells her that she is alive and asks her to come. Baekryeon goes alone to the address where Eun-seo is.

Baek-ryeon sees her past life during her surgery, and is confused because the angel in her past life resembles Sang-hyuk. Meanwhile, Jae-hee begins to have doubts about Sang-hyuk's identity, and the legal hypnotist Cheong-il gives Sang-hyuk Baekryeon's unofficial hypnosis records.

Jae-hee informs Baek-ryeon that Sang-hyuk is not human, and Baek-ryun suddenly remembers Sang-hyuk's missing hand. Meanwhile, she realizes that she forgot to climb the mountain one last time so she goes to Inwang mountain to complete her mission. Jae-hee and Sang-hyuk also head there to find her.

The police arrest Kim Myeong-sik as the prime suspect who finally confesses that he killed Go Eun-seo. He claims that there will be no more victims since he will be locked up. Meanwhile, Jeong-ah's parents come to Baekryeon's animal hospital, and Baekryun suddenly sheds tears as she hears the story of their daughter's disappearance.

Just before his final “metamorphosis”, Sang-hyuk finds out who Baek-ryeon is and feels very confused. After hearing that once he enters the transformation phase, nobody can tell when he will come out, Baek-ryeon fears that Sang-hyuk will disappear forever. Jae-hee happens to see a portrait of Sang-hyuk and So-hee, and he visits Sang-hyuk to ask who the woman in the painting is.

When Kim Myeong-sik, whom everyone identified as the culprit, gets murdered, the case becomes even more mysterious. Baek-ryeon hears the criminal's voice in her dream, which reminds her of some voice she heard in real life recently. Meanwhile, Sang-hyuk conducts a large-scale search of the Jongseo-gu area with several clues.

Baek-ryeon now faces the very same ill fate as she had in her past life. 500 years ago, her life was spared thanks to Sang-hyuk who turned her fate around but as a punishment for intruding in the divine business, he has been bound to go through several metamorphosis for 5 centuries. Meanwhile, Baek-ryun confronts a huge crisis due to Song Young-cheol's scheme.