Do Eun, Yi Chul's mistress, exposes herself and their baby on her social media on purpose, and the whole world finds out about their affair. Ji Chang and Hye Won are on Soo Hyang's side for the divorce trial and try their best to comfort her. Meanwhile, Ji Chang prepares a gift for Hye Won before their wedding.

Ji Chang promises Hye Won to find her long-lost sister, Hye Ji, no matter what. Hye Won discovers Yi Chul has been embezzling company funds under a shell company for two years. Meanwhile, Do Eun is curious about Ji Chang's fiancé and wants to meet her.

Do Eun plans to meet her soon-to-be daughter-in-law and rear-ends Hye Won's car to get things started. She then buys an art piece from her gallery. To learn more about the painting, Do Eun offers to have dinner together. At the dinner, Eun notices the pendant necklace around Hye Won's neck that she once shared with her biological sister.

Do Eun realizes Hye Won is her biological sister, whom she separated from when they were young. Meanwhile, Hye Won is confused about why Do Eun left in a rush from their dinner. Later, Hye Won learns Do Eun is Yi Chul's mistress and becomes furious.

Kyung Ja appears unexpectedly and ruins Hye Won and Ji Chang's wedding while Do Eun watches from the sidelines. However, Do Eun sees Min Tae, her father, and she begins to remember the past. Meanwhile, Myung Ae can't believe the disgrace Hye Won brought to the family and scolds Ji Chang.

After ruining Hye Won's wedding, Do Eun plots another scheme to bring her down with Kyung Ja. Hye Won and Ji Chang return home without going on a honeymoon, and Hye Won even sees Do Eun in her dream. While Myung Ae gives Hye Won a hard time at home, Do Eun sends a text message to Hye Won.

Do Eun suggests to Hye Won that they meet and talk in person. Do Eun sends her a photo of her necklace to convince her that she is her younger sister, Hye Ji. Hye Won waits for Hye Ji at the mineral spring, but a man shows up instead of Hye Ji.

Do Eun becomes furious after the protest in front of the Boram Childcare Facility. Do Eun suspects Hye Won is the one responsible for the protest and calls her to meet. Meanwhile, breaking news of Yi Chul's large donation to the Boram Childcare Facility by using a shell company airs, along with Do Eun's position in the facility.

Hye Won is disappointed after learning that the phone number that said it was Hye Ji is from a burner phone. Meanwhile, Myung Ae visits the temple and discovers from the monk that Yi Chul will have another child of great importance, and Do Eun takes off to get some air.

After learning that Soo Hyang will be holding a talk concert, Do Eun appears at the event and asks a question during the Q and A time. Hye Won is astounded by Do Eun's appearance and tries to remedy the situation. Meanwhile, Soo Hyang realizes the woman is Do Eun.

Since Young Ju and Jang Gun cannot reach Do Eun anymore, they change their target to Hye Won. To bring Hye Won down, Do Eun runs a background check on Judan Foundation for Arts and finds out about Dan Ung, who signed with the gallery. Not long after Do Eun's confrontation, another shocking news about Soo Hyang breaks out.

Dan Ung frames Soo Hyang for sexual assault and disappears. No matter how hard Hye Won tries to reach him, he is nowhere to be found. Meanwhile, Ji Chang suspects Do Eun, so he wants to meet her in person to reveal the truth.

Ji Chang encounters Do Eun directly, only to find that she doesn't match the image of recklessness he had anticipated. Upon Ji Chang's return, Hye Won expresses her disappointment in his apparent favoring of Do Eun. Meanwhile, Soo Hyang intends to pay Attorney Song a visit.

Hye Won tries to find Dan Ung, who has gone out of contact, to no avail. She returns home but gets further frustrated when Ji Chang thinks the opposite about Do Eun. To make matters worse, Do Eun tells Yi Chul about what Hye Won did to her when they coincidentally met and gets Hye Won in trouble.

Hye Won and Ji Chang are traumatized by Yi Chul and Soo Hyang's divorce, and Ji Chang starts to resent Do Eun even more. However, Myung Ae invites Do Eun over to their place. Meanwhile, Jang Gun and Young Ju visit Hyangdan Agency to find Hye Won and run into San Deul.

Hye Won and Do Eun meet again when Do Eun visits her in-laws at home. Do Eun shares surprising news, and Hye Won feels uncomfortable around her. The memory of their childhood unexpectedly overtakes Do Eun, but she tries to pull herself together for revenge. Meanwhile, Hye Won and Ji Chang grow apart after Do Eun joins the family.

Hye Won is stunned to learn that Dan Ung has departed the country, particularly shocked when she discovers his destination is Mauritius. Do Eun's fake pregnancy approaches revelation as she's guided, somewhat reluctantly, to the OB-GYN. Meanwhile, Sung Yoon establishes a law office conveniently close to San Deul’s tteokbokki spot.

Do Eun uses her wits to overcome the crisis of her fake pregnancy getting exposed. Meanwhile, Hye Won searches for evidence that Do Eun was behind the incident involving Soo Hyang. She resorts to apologizing to Do Eun to get the answers she needs.

Hye Won finally meets Lim Dan Ung face-to-face. After acquiring the evidence that would clear Soo Hyang's name, she hands it to Soo Hyang. However, Soo Hyang tells Hye Won that she will take care of it and calls Do Eun to meet.

Now that Soo Hyang has the recorder from Dan Ung, she decides to talk to Do Eun in person. She asks Hye Won to keep it a secret from Ji Chang as she wants to handle it on her own. When Soo Hyang calls Do Eun to confront her with the evidence, Do Eun flips out and asks for forgiveness.

Before Soo Hyang exposes the truth, she passes away due to a heart attack. Do Eun brazenly attends the funeral in a mourning dress, which makes Hye Won and Ji Chang infuriated. Hye Won quickly leaves the funeral after she gets a call from Dan Ung, and Do Eun tries to stop her. Meanwhile, Sung Yoon attends the funeral after hearing the news and runs into Hye Won.

Hye Won heads directly to meet Lim Dan Ung, but upon arrival, she is met with a disturbing scene. Despite the confusion, Hye Won gathers her resolve to uncover the truth behind the suspicious deaths. Meanwhile, Myung Ae instructs Hye Won and Ji Chang not to conceive a child until Do Eun delivers her baby, but it may be a bit too late.

After bumping into Hye Won at the pharmacy, Sung Yoon notices that Hye Won is pregnant. However, she doesn't recognize him and goes on her way. Meanwhile, Do Eun moves in with the family and begins to get under Hye Won's skin. Their new life under the same roof begins, but Hye Won has no intentions of giving in to her.

Young Ju and Min Tae run into each other and ask about their daughters, Hye Won and Hye Ji. Min Tae lies to her by saying Hye Won is studying abroad to protect Hye Won from her. Meanwhile, Do Eun lies to Ji Chang about what happened between Soo Hyang and her at the hotel, and now, she wants to set up a fake miscarriage and put the blame on Hye Won.

Do Eun gets anxious after she finds out Hye Won is pregnant. Moreover, Myung Ae makes it clear to Do Eun that she will only let her join the family after she gives birth to Yi Chul's child. Therefore, instead of faking the pregnancy, Do Eun changes her plan to actually get pregnant this time. Meanwhile, Sung Yoon wants to help Hye Won with Dan Ung's case.