Kim Jinseo and Mo Yoonhee are high school classmates and rivals whose different family backgrounds shaped their characters and their paths towards love and success in adulthood. Jinseo develops a warm and cheerful personality as well as superior intellectual ability, while Yoonhee becomes a beautiful woman with fatal charm. Both women love Lee Sanghyun, an extremely kind but indecisive man who used to date Yoonhee but later married Jinseo. When Yoonhee's husband, Sung Eunpil, dies under suspicious circumstances, Jinseo finds herself becoming involved in the investigation. The process is complicated when the young homicide detective Kang Shinwoo becomes romantically interested in Jinseo.
Episode 1
Jinseo and Sanghyun plan to have a family picnic and a restless night. That day in the early morning, Sanghyun goes to Yunhi's villa with her to deal with the disappearance of her husband.
Episode 2
Jinseo urges Sanghyun to tell the truth after Yunhi tells her that Sanghyun was with her on the night of Eunpil's death. After hearing that dinner for 3 people was prepared that night at the villa, Eunsuk tries to find out who the third person was.
Episode 3
Sanghyun is confused when Jinseo tells him he has cancer and Jinseo gets her doctor friend to go along with her lie.
Episode 4
When the truth comes out, Sanghyun is confused. Yunhi asks Hisu if it is okay for a doctor to be messing with people's lives. Yunhi takes an angry Sanghyun and a shocked Dulnam to Sanghyun's home behind Jinseo's back.
Episode 5
Jinseo and Shinu learn that Lee Junhi is not a woman, but a middle-aged man. Yunhi and Sanghyun become angry after seeing a picture of Eunpil and Jinseo being friendly together. While discussing Jinseo and Eunpil, Sanghyun confronts Jinseo.
Episode 6
Jinseo finds Eunpil's walnuts at the site of the accident and claims it was murder, but Shinu is wary of Jinseo's intentions. Lee Junhi tells Yunhi that Eunpil died in a car accident and not to worry about it.
Episode 7
Jinseo learns that Junhi kidnapped Minjo. Jinseo and Sanghyun find Yunhi to ask about Junhi's whereabouts, but Yunhi claims not to know. Jinseo says she will definitely find out who killed Eunpil.
Episode 8
Jinseo kneels before Yunhi and begs her to return Minjo to her, saying she will let her have Sanghyun and give up on finding Eunpil's murderer.
Episode 9
Shinu and Jinseo learn Lee Junhi is actually Yunhi's father, Mo Junha. Sanghyun becomes angry when he sees Shinu and Jinseo talking. Sori goes to Jinseo to apologize for what happened in the past.
Episode 10
Junha asks Jinseo if she trusts Sanghyun and he tells her that he saw Sanghyun at the villa the night of Eunpil's death. When Jinseo asks Yunhi about the truth of what happened, she says her only crime is acting like she doesn't know anything.
Episode 11
Shinu finds out Sanghyun got a speeding ticket the night of Eunpil's death. Shinu tries to find out Sanghyun's whereabouts by asking Jinseo. However, after seeing how nervous she was, he doesn't ask.
Episode 12
Yunhi goes to Junha, who claims that he killed Eunpil and disposed of his body for her. To make sure this case goes unsolved, he says they need to put suspicion on Sanghyun.
Episode 13
After finding the broken wine bottle, Shinu takes Yunhi and Sanghyun to the police station for further questioning. Jinseo implores to Sanghyun that if he wants to survive this, he has to tell the complete truth and not fall for Yunhi's tricks.
Episode 14
After Dulnam learns that Yunhi framed Sanghyun as the murderer, she goes to Yunhi to give her a piece of her mind. She also punishes Sanghyun for not trusting Jinseo. Yunhi threatens Eunsuk with Sumin and speeds up the inauguration ceremony.
Episode 15
Yunhi goes to Junha's home. After seeing the drawings of her youth, she finally understands her father's feelings.
Episode 16
Eunsuk refuses to bury Yunhi in the Sung family cemetery. Eunsuk finds Sumin's whereabouts and visits the nursing home where Sumin is staying.
