In The Frog, Yoo Seong-a, played by Go Min-si, is the lead antagonist who refuses to leave Yeong-ha’s house.
Yoo Seong-a is an artist from a wealthy family. However, her father does not like her paintings, believing that people only buy them because of his influence.
Seong-a ends up marrying Jae-sik but does not find happiness with him either. Although Jae-sik’s son, Si-hyeon, loves Seong-a, she does not want him in her life.
She constantly doubts whether Jae-sik married her out of love or simply to provide a mother for his son. Her insecurities eventually lead her to commit a heinous crime.
Killing an innocent child
Seong-a falsely accuses Jae-sik of domestic abuse, resulting in him going to prison. She then decides to test whether Jae-sik would have married her if he did not have Si-hyeon.
To do that, she rents Yong-chae’s vacation home in the countryside, where she plans to kill Si-hyeon, the child she never loved. Yong-chae’s air conditioner breaks down, so he arranges for her to stay at Yeong-ha’s house instead.
That night, Seong-a kills Si-hyeon, dismembers his body, and meticulously cleans Yeong-ha’s bathroom to eliminate any traces.
She leaves early the next morning and gives Jae-sik the body of another child, claiming that Si-hyeon died in an accident.
Months later, she returns to rent Yeong-ha’s house, having become attached to the place after committing murder there. Yeong-ha reluctantly allows her to stay.
As Yeong-ha pretends not to recognize her, Seong-a realizes that he suspects her. Her suspicions are confirmed when he eventually confronts her about Si-hyeon’s death.
She discovers that Yeong-ha has dashcam footage showing her leaving the house without Si-hyeon and that he had destroyed all other evidence against her.
Seong-a then starts taking advantage of the fact that Yeong-ha covered up her crime. She torments him relentlessly, fully aware that he cannot go to the police no matter what she does.
Seong-a’s brutality and unchecked violence
Seong-a wishes to buy Yeong-ha’s house and starts making changes to it without his consent. When Yeong-ha can no longer tolerate her behavior, he decides to go to the police with the dashcam footage and a recorded confession.
He is prepared to face the consequences of covering up Seong-a’s crime, but Seong-a hits him with her car to stop him from taking the evidence to the police.
She steals the evidence, leaving Yeong-ha with no leverage against her. This marks the beginning of a psychological war between them over the ownership of the house.
Seong-a even involves Officer Kim but kills him the moment he finds the evidence she had stolen from Yeong-ha. A desperate Yeong-ha then agrees to sell her the house but disappears for a while.
During his absence, Yong-chae comes to visit and is stabbed by Seong-a when he threatens to call the police on her. Seong-a keeps him locked in the basement.
To force Yeong-ha to return, Seong-a kidnaps his pregnant daughter, Ui-seon, drugs and injures her, and keeps her locked in a bag.
She only releases Ui-seon when Yeong-ha returns and agrees to help her bury Officer Kim’s body, unaware that Yeong-ha is now working with the police.
This leads to Seong-a’s arrest, but the police cannot keep her in custody for long, as there is no solid evidence against her. In fact, she appears to be a victim of domestic abuse and mental illness.
Once released, she continues to ruin lives. Her father, realizing that his daughter is a murderer who cannot be controlled, asks Jae-sik to kill her to prevent further damage to his reputation.
Seong-a is then killed by Jae-sik. The police also find Officer Kim’s body, which provides concrete evidence that Seong-a is a murderer. Ultimately, she faces justice for her crimes, but not before inflicting pain on many others.
Also Read: The Frog recap and ending explained