Dan Dan grows up being told that her birth mom is dead but still becomes a hard-working young woman. One morning, she overhears her stepmom and stepbrother talking about something that sounds like trouble for the family. Meanwhile, Young Guk is a single father of three kids after losing his wife two years ago. He asks a friend to help him find a live-in tutor.

Dan Dan takes Young Guk for a handsome psychopathic criminal, like in the movies, and she hits him in the head with her water bottle. Young Guk ends up with a gash on his forehead and is baffled by Dan Dan's plea for forgiveness. Meanwhile, Guk Hee suggests Dan Dan go in for an interview to become the live-in tutor at Young Guk's house.

Dan Dan gets hired to work as the live-in tutor at Young Guk's house, thanks to the help of Sa Ra. However, she gets into trouble on her first night on the job. Meanwhile, Sa Ra gets invited to a fancy restaurant by Young Guk and begins to get her hopes up. As Dan Dan tries to get used to living and working in Young Guk's household, she runs into an unexpected familiar face.

Dan Dan and Soo Cheol realize that they work in the same household and worry that their employer might think they are up to something suspicious. Yeon Sil tries to persuade Dan Dan to leave her position, but Dan Dan refuses. Meanwhile, Young Guk decides to let his late wife rest in peace, and he has her things cleared away.

Young Guk's strict nature with his kids makes his relationship with Se Jong worse than ever. Young Guk enlists Dan Dan's help to resolve the matter. Although they bicker about how to handle the kids, Dan Dan's advice makes the kids grow brighter by the day. Meanwhile, a mysterious man appears before Sa Ra, which makes Ki Ja suspicious about her daughter's past.

Young Guk and Jae Ni fight when he mistakes Jae Ni's new friend, who happens to be a boy, as her boyfriend. Dan Dan helps the father and daughter make up, and Young Guk feels grateful. Meanwhile, Yeon Sil's mom, brother, and niece return from working abroad for five years. She asks them to come to the annex at Young Guk's house and trouble ensues.

Young Guk's family treats Soo Chul as if he were a parasite and a fraud, and they kick him out. As Dan Dan watches her dad endure such humiliation, she decides she must leave her job as well. The children see how sad Dan Dan is, and they come up with a plan to cheer her up. Meanwhile, Anna begins looking for a way to get back in touch with her daughter.

Soo Chul finds out that Dan Dan got an advance on her salary and gave it to Yeon Sil. He becomes upset and goes to see Dan Dan to return the money. However, he is only met with more disappointment when Dan Dan asks to continue living as strangers. Meanwhile, Anna decides to stay at Young Guk's for a while to be close to Dan Dan.

Dan Dan is upset that she has to lie about going to see her dad in the hospital and ends up blurting out the truth to Young Guk. When Young Guk hears of her relationship to Soo Chul, he becomes angry that she was untruthful and fires her. Sa Ra is glad to see Dan Dan go and takes this chance to get on Dae Ran's good side. Meanwhile, the kids miss Dan Dan dearly.

When Dan Dan returns to help console Se Jong and continue working at Young Guk's house, Sa Ra feels threatened by her. Se Ryeon gets drunk and barges into Dae Bum's house, asking him to take her back. The two families end up clashing once again. Meanwhile, Dan Dan joins Young Guk and the kids on a trip to their vacation home for Se Chan's birthday.

Young Guk finds Dan Dan in the woods with a sprained ankle. Sa Ra becomes angry and jealous when she witnesses Young Guk carrying Dan Dan on his back. Meanwhile, Dal Rae sees a photo of Mi Sook and her younger brother and is reminded of Soo Chul's childhood photo. Later on, Young Guk invites Dan Dan out to a restaurant.

Dan Dan and Young Guk realize that they have a past connection. When Sa Ra sees how close Dan Dan and Young Guk are getting, she is overcome with jealousy. Meanwhile, Se Ryeon meets the man Dae Ran wants her to marry. While on her date, Se Ryeon runs into Dae Bum in his food truck. Finally, Dae Ran and Sa Ra scheme to have Dan Dan thrown out.

Dan Dan confesses her feelings for Young Guk in a drunken state which sends her into a frenzy the next morning. It makes her even more nervous to face Young Guk, and Young Guk also starts to notice Dan Dan in a different way than before. Meanwhile, Dae Ran and Sa Ra decide to lie about the dementia test results and continue to harass Dan Dan.

Dan Dan gives Young Guk time to make up his mind about her until the next day at midnight. Young Guk contemplates long and hard about what to do. Meanwhile, Dae Bum realizes that Se Ryeon is about to get married to a two-timer and tries to stop her, leaving Se Ryeon feeling confused. Later on, Sa Ra witnesses Dan Dan with Soo Chul and tries to use it to get Dan Dan kicked out.

Sa Ra confesses her feelings for Young Guk, making him decide that they cannot work in the same house anymore. As Sa Ra resigns and leaves Young Guk's house, Dan Dan and Young Guk's secret relationship starts to get more serious. Meanwhile, Sa Ra calls a driver to take her home after she has too much to drink, and Gun shows up for the job.

Young Guk confesses to Dan Dan that he couldn't tell Anna about their relationship, and the two agree to take things slowly. However, Young Guk continues to worry that Dan Dan might get hurt by other people's comments about their relationship. Meanwhile, Kyung Seok's girlfriend shows up just as Se Ryeon's wedding is about to begin.

Dan Dan returns home alone after waiting to meet Young Guk. She is shocked to hear that he is still not back from his hiking trip. Young Guk's family and friends call the police and desperately search for him, but Dae Ran imagines making Se Ryeon the acting chairman if Young Guk isn't found soon. Later on, Young Guk comes home but in a shocking state.

Sa Ra and Dae Ran decide to lie to Young Guk and tell him that he and Sa Ra were engaged to be married. As Young Guk feels confused, Dan Dan thinks he was two-timing her. She decides to quit her job and tells the children goodbye. However, a small part of Young Guk's memory comes back, making Sa Ra more anxious than ever.

The conflict between Sa Ra and Dan Dan escalates as Young Guk’s sons get involved. While Sa Ra clearly favors Se Jong, Dan Dan tries to treat both Se Jong and Se Chan equally. Meanwhile, Soo Chul gets fired from work due to the company’s financial problems. Yeon Sil becomes devastated by this and searches for someone to help them out. With many events, everyone in Soo Chul’s family is going through a hard time.

Young Guk thinks that he hurt Sa Ra by cheating on her with a younger woman, so he wants to make it up to her. He plans a big proposal at the vacation home and takes her there. Meanwhile, Dan Dan becomes saddened when she hears about Young Guk's proposal plans. She makes up her mind to go to the States with Anna.

Young Guk becomes confused after having kissed Dan Dan on the lips, and Dan Dan, who finds it inconceivable that their lips touched, becomes bothered by it. Meanwhile, Dae Ran gets annoyed with Ki Ja and Sa Ra bickering about their circumstances. To cool things down, she gives Young Guk the advice of getting engaged to Sa Ra, and Young Guk thinks about it.

Jealousy overcomes Young Guk after seeing Dan Dan and Hyun Bin affectionately together. Using coincidence as an excuse, he tries to spend as much time with her as he can. Sa Ra attempts to get close to the 22-year-old Young Guk, but it's not as easy as she thought it would, and she becomes irritable. Meanwhile, Young Guk participates in Se Jong's sports day.

Young Guk feels guilty about liking another woman when he is just about to get engaged. He tries to make himself like Sa Ra but finds it tough to get Dan Dan off his mind. Meanwhile, Sa Ra is appalled after learning the newly dispatched diver is Cha Gun and will work at Young Guk's house.

As the day of her engagement draws near, Sa Ra feels anxious about Gun's presence in Young Guk's house. She decides she must do something about it and asks to see him. Meanwhile, Young Guk can't hide his feelings for Dan Dan any longer and confesses his feelings to her. However, Dan Dan's reaction is not what he expected.

Young Guk's kids receive a great shock when they find out about Young Guk and Sa Ra's engagement. Se Chan even leaves a note saying he refuses to accept Sa Ra as his new mom and disappears. Meanwhile, Sa Ra asks Dan Dan to help persuade the kids about her engagement to Young Guk. Although it hurts her to say it, Dan Dan talks to Jae Ni and Se Chan to support their dad.

Young Guk continues to get bits and pieces of his memory back. He wonders why those memories include Dan Dan and asks her about it, but Dan Dan refuses to admit that there was ever anything between them. Meanwhile, Sa Ra grows more anxious as Young Guk seems close to regaining all of his memories. She decides to do something before he does.

Young Guk regains his memories, throwing Sa Ra and Dae Ran into a frenzy. Dae Ran begs Sa Ra not to tell Young Guk about her involvement in their scheme, but Sa Ra declares she will not give up on marrying Young Guk. Meanwhile, Se Chan and Se Jong decide that they would rather have Dan Dan as their new mom than Sa Ra. They start to play Cupid between Young Guk and Dan Dan.

Soo Chul stays with Anna on the day of her surgery and comforts her. When she begins to show her affection for him, Soo Chul feels conflicted. Meanwhile, Sa Ra releases an article about her engagement with Young Guk. Although Young Guk accepts the fact that he must acknowledge the engagement as well, he is upset and ends up spilling his true feelings to Dan Dan in a drunken state.

Anna goes to Yeon Sil and asks her to persuade Soo Chul to come and work in the US with her. After hearing the salary Soo Chul would get if he took the offer, Yeon Sil pushes Soo Chul to accept. Meanwhile, the conflict between Young Guk's kids and Sa Ra worsens. Dan Dan decides not to hold her feelings back and to stay by Young Guk's side.

Yeon Sil and Anna finally convince Soo Chul to go work in the US, but now Dan Dan refuses to go. As Young Guk tries to make Dan Dan leave with Anna, Se Chan and Se Jong come up with a plan to make Young Guk and Dan Dan grow closer once again. However, when the boys' plan goes up in smoke, Young Guk discovers how Sa Ra has been treating the kids behind his back.

After the fire at the vacation house, Dan Dan returns to Soo Chul's place on sick leave given to her out of consideration by Young Guk. However, Young Guk ends up heading there to pick up the kids, who had gone to visit her at Soo Chul's house. Meanwhile, Yeon Sil explains to Soo Chul about the baby pictures that look similar to Dan Dan she saw at Anna Kim's house, and Dan Dan expresses her longing for her biological mother.

As Dan Dan keeps trying to make Young Guk admit his feelings for her once again, Young Guk continues to ignore her efforts. Meanwhile, Soo Chul's suspicions for Anna grow to the point that he decides to secretly run a DNA test on Anna and Dan Dan. After discovering Anna's identity, Soo Chul flies into a rage and tells her to stay away.

Dan Dan finds out that her birth mother is alive. She asks Soo Chul to tell her about her birth mom, but he refuses to do so. Dan Dan decides to ask Anna for help since her birth mom is said to have gone to the US. Soo Chul tells Anna that she must leave as soon as possible. Meanwhile, Young Guk promises Dan Dan that he will help her find her birth mom.

Young Guk insists that he and Dan Dan maintain a professional relationship only. However, his feelings for Dan Dan keep showing inadvertently, and Dan Dan wants him to admit he still has feelings for her. Meanwhile, Dae Bum and Se Ryeon's relationship is tested when the two realize they might not be able to bridge the gap between their two very different worlds.

Dan Dan and Young Guk finally admit their feelings for one another and start dating, although they have to keep their relationship a secret for now. As the prospects of Se Ryeon and Seung Ho's marriage become more realistic, Seung Ho goes to see Dae Bum and tries to give him a wad of cash. Meanwhile, Sang Gu reappears before Sa Ra and demands to know where his son is.

Se Ryeon hears about the rumor that Seung Ho has a child and asks Dae Ran if it's true. Then, Mi Sook tells Se Ryeon the truth about Seung Ho and that Dae Ran asked to have her set up with him. The truth shocks Se Ryeon to the point where she decides to give it all up. Meanwhile, Young Guk finds himself leaning on Dan Dan more and more, especially when life gets hard.

Young Guk finally asks Dan Dan to officially be his girlfriend. Although they are overwhelmed with joy, they’re still nervous about how to tell the news to the people around them. Meanwhile, Ms. Wang goes over to Dae Bum’s family and makes a scene. She claims that they are scheming to steal Se Ryeon’s shares of the company. If she finds out about Young Guk and Dan Dan, the situation will only get worse.

Young Guk tells the news to Anna. Unlike his thoughts, Anna does not understand their relationship. She strongly claims that the two dating is not right. Moreover, Dan Dan’s father finds out about this as well. As a parent, he cannot accept his daughter going out with a much older guy who already has three children. The future of Young Guk and Dan Dan’s relationship seems darker than ever.

Anna witnesses Young Guk and Dan Dan sharing a tender moment outside of his office. She tells Young Guk off, saying he should consider what people might say. Young Guk feels confused and hurt by Anna's reaction. Meanwhile, Soo Chul is adamant that Dan Dan break up with Young Guk, even though Yeon Sil tries to talk him out of it.

Dan Dan and Young Guk decide to tell the kids about Dan Dan's departure. The kids are sad to hear the news, but they try their best to be mature about it. They say goodbye with a farewell trip and a promise to see each other again in three years' time. Meanwhile, Yeon Sil tails Soo Chul when she figures out something suspicious is going on between him and Anna.

Dan Dan goes to see Se Jong who is suffering from separation anxiety. He gets better as soon as she reassures him and everyone is relieved. However, Soo Chul becomes furious at Young Guk for calling Dan Dan out in the middle of the night and spews harsh words at him. Meanwhile, Dan Dan goes to Anna's apartment while preparing for a fashion show and stumbles upon a photo album.

Dan Dan realizes that Anna is her birth mom and that Soo Chul tried to send her to the US while knowing this fact. Feeling shocked and hurt, Dan Dan storms out of the house. Meanwhile, Sa Ra is taken by surprise when Gun takes her to his humble family home. After turning him down, she goes back to Young Guk's house, using the flowers as an excuse once again.

Young Guk recalls a fragment of a memory from when he thought he was 22 years old and becomes anxious that he might have mistreated Sa Ra. Dae Bum and Se Ryeon run into each other and rekindle their love. Yeon Sil gets worked up about their relationship but changes her tune once she hears about Se Ryeon's shares. Meanwhile, Sa Ra continues to feel nauseous and takes a pregnancy test.

Sa Ra barges into Young Guk's house and announces that she is pregnant with Young Guk's child. Young Guk feels confused about it all but ends up letting her move back in when she shows up with all of her belongings. Meanwhile, Dan Dan is in great shock and moves out. Finally, Dae Bum and Se Ryeon have their wedding.

Dan Dan thinks Sa Ra might be lying about her baby being Young Guk's child. She goes to talk to Young Guk, but he refuses to listen. Still, Young Guk spends night after night drinking, and Se Jong's separation anxiety gets worse. Jae Ni decides to take Se Jong to Dan Dan's house. When Sa Ra finds out, they get into a fight.

Young Guk gets a flashback of being with Sa Ra as his 22-year-old self. He confronts her about her lies and demands that she move out. However, Sa Ra refuses to budge. Meanwhile, Dan Dan has a hard time letting Young Guk go, and it's made harder by Se Chan and Se Jong wanting to stay with her. But when Sa Ra shows up at her family home, Dan Dan makes up her mind.

Young Guk finally regains all of his memories but doesn't want Dan Dan to get mixed up in his complicated life anymore. Soo Chul wants to send Dan Dan abroad before she finds out about Young Guk's memories coming back and arranges a meeting between her and Anna. Meanwhile, Sang Gu gets suspicious of Sa Ra's behavior around Se Jong and runs a DNA test.

Sang Gu continues to threaten Sa Ra for money, and when that doesn't work, he decides to use Se Jong as bait. Se Jong nearly gets into an accident while running away, and Dan Dan gets injured while saving him. Meanwhile, Ki Ja gets caught for stealing Dae Ran's gold and money, but this leads to Young Guk finding out about the whereabouts of his mother's diamond ring.

Se Chan and Se Jong get excited to see Dan Dan back at their house for a job interview, but Young Guk turns her away. Soo Chul tells Anna that she must get surgery and go on living for Dan Dan's sake and decides to stay by her side throughout her treatment. Meanwhile, Mi Sook finds out that Jun O and Mi Rim have been living together.

Young Guk finally realizes that he was wrong to break Dan Dan's heart and tries to win her back. As Mi Sook continues seething over Jun O and Mi Rim's relationship, Jun O declares that he won't see Mi Sook anymore until she apologizes to Mi Rim. Meanwhile, Yeon Sil sees Soo Chul and Anna together and accuses them of having an affair.