After their father's death, Sun Hee and Do Hee have been living completely different lives. Sun Hee is known to be a fool due to her way too kind nature. On the other hand, Do Hee becomes a top stewardess and lives a fancy lifestyle. One day, something unpleasant happens to Do Hee.

While dropping by Do Hee’s house to give her some side dishes, Sun Hee is attacked by a masked man. He tells her to bring something and that he’ll give her four days. Sun Hee tells Do Hee about this, but Do Hee tells her that it’s just one of her ex-boyfriends and to mind her own business.

Do Hee comes to Sun Hee's place and collapses. She asks Sun Hee for a favour, and Sun Hee decides to pretend to be her sister and goes to work. To make matters worse, she is forced to fly as well. During the flight, she saves the chairman of Donghae Airlines, Oh Pyung Pan, and even runs into the famous pilot, Song Woo Jin.

The plane suddenly encounters turbulence, and Sun Hee is terrified. However, she notices that the chairman is missing and looks for him. She finds him in the restroom after he hits his head and helps him to get back to his seat. While helping him, she hits her head and faints. Woo Jin hears that she’s unconscious and checks up on her. Upon waking up, they accidentally kiss, and Woo Jin is more than just flustered.

Sun Hee moves into the share house in place of Do Hee. There, she meets Woo Jin once again. He tries to close down the share house, and the two start to clash. She is shocked after finding out that her twin sister, Do Hee, likes him.

Ok Jeong, Sun Hee's mother-in-law, moves into Sun Hee's house and calls her whenever she is out for too long. When Sun Hee comes home, Ok Jeong demands that she discloses everything she did while she was outside. Meanwhile, Sun Hee is determined to find the culprit who attacked her sister and goes through the contact list of Do Hee's phone.

After seeing how furious Woo Jin is at her, Sun Hee gives up on Do Hee and his relationship and focuses on catching the culprit who attacked Do Hee. She finally finds a lead that will help her take one step closer to the culprit. Meanwhile, Ok Jeong suspects Sun Hee of committing adultery.

Ok Jeong and Chun Ji video call Sun Hee and see Woo Jin behind her. They immediately confirm their suspicions of her having an affair and tell Chun Dae about it. Meanwhile, on the flight back to Korea from Japan, Sun Hee encounters a sick, elderly woman who vomits. Without any hesitation, Sun Hee cleans the vomit and comforts her. Upon seeing this, Ye Bin considers this odd.

Sun Hee is once again attacked by the masked man in front of the share house. At that moment, Woo Jin sees them and saves her. They go to the police station, and Sun Hee thanks him. Woo Jin tells her that if she is so thankful, she should move out of his house.

Ok Jeong, Chun Dae, Chun Ji, and Moon Sook follow the GPS tracker to find out where Sun Hee is. They arrive at Woo Jin's house, and their suspicion of her having an affair is confirmed. However, Sun Hee pretends to be Do Hee and counter-attacks them. She even threatens to call the police on them for breaking in.

Woo Jin corners and questions Sun Hee about why she claimed that they were dating. Not knowing what else to do, Sun Hee tells him that it is because she likes him. Woo Jin, who has been getting strange feelings towards Sun Hee, is even more confused. Meanwhile, Sun Hee says that she cannot demand the flight attendant to hand in her resignation letter.

Tae Ree bans Sun Hee from flying, and Sun Hee begs her to lift the suspension. Just when Tae Ree is about to slap her, Woo Jin interferes and grabs Tae Ree by the arm. He then tells her that they are in fact in a relationship.

Tae Yang tells Woo Jin that he will no longer allow him to steal everything that is dear to him. He tells Woo Jin to stay away from Sun Hee. Woo Jin acts nonchalantly, but he is bothered by this. Meanwhile, Moon Sook goes to the department store to get a refund for the present Chun Dae got her, only to find out that he may be seeing someone.

Woo Jin confesses his feelings for Sun Hee and also recruits her to be a main cabin crew for One Air. Sun Hee is glad that she did not ruin the relationship between Woo Jin and Da Hee. However, Cho Rong tells her that the one he fell in love with is not Da Hee but Sun Hee. Meanwhile, Kang Min decides to hold hands with Ye Bin.

Chun Dae's double cheating is disclosed to his entire family, Moon Sook, and Sun Hee. Sun Hee is gravely hurt and feel betrayed. Meanwhile, Woo Jin runs into Sun Hee who is sharpening a kitchen knife in the middle of the night. He misreads the situation and believes that she is mad at him for not taking any actions after confessing his feelings for her.

Ye Bin tells Woo Jin that Do Hee has alcohol related dementia. Upon hearing this, Woo Jin is bewildered. Meanwhile, Chun Dae apologizes to Sun Hee for cheating on her with two other women. He swears never to cheat ever again. However, Sun Hee's heart is too broken, and she does not know what to do.

Kang Min urges Pyung Pan to flee for the time being, and he agrees to do so. After sending him off, Kang Min reports his fleeing. Now, Donghae Airlines is in Tae Ree's hands, and she can do whatever she wants. Meanwhile, Ye Bin finds out that Do Hee does not have alcohol related dementia.

In order to cut the food production cost for One Air, Sun Hee and Woo Jin go to the fish market together. There, they buy fish, and Sun Hee fillets it. Woo Jin is surprised to see this side of her and also falls in love with her once again. Meanwhile, Min Ji demands that Chun Dae pays for the things he bought for his family with her card.

Sun Hee catches Chun Dae attending Soo Hyun's husband's funeral as a "host". He explains that he's just doing this out of friendship and that there is nothing going on between Soo Hyun and him. However, Sun Hee is shocked that he would dare to meet Soo Hyun once again. Meanwhile, Tae Yang finds out that the woman he fell in love with is not Do Hee, but Sun Hee.

Pyung Pan is brought to Woo Jin, and he is having severe stomach pains. Not knowing what to do, Woo Jin asks Sun Hee for help, and she does her best to help Pyung Pan. Meanwhile, on her way home from a flight, Ye Bin spots Woo Jin and Sun Hee helping Pyung Pan into a car and takes a photo.

Sun Hee pretends to be Do Hee and barges into Min Soo Hyun's restaurant with Sun Hee's co-workers. She surprises Soo Hyun and Chun Dae with evidence of their adultery. Furthermore, she tells her co-workers that they can eat there as they please and that Soo Hyun will pay for the cost. Meanwhile, Pyung Pan asks Woo Jin to take care of the company for him.

Chun Dae hands Sun Hee, whom he thinks is Do Hee, a divorce paper, saying he already signed it. He tells her that he chose his wife solely because she was nice, but now, Do Hee has ruined him. Sun Hee is hurt to hear these words. Meanwhile, while preparing for the test flight, One Air crew hears the news about the test flight getting cancelled and One Air being sold to Chanmi Food.

Ok Jeong goes to Sun Hee's place to beg her to nullify the divorce. She also asks her whether she will continue to pay for her insurance even after the divorce. Sun Hee stands up for herself. She tells Ok Jeong that Chun Dae has already moved in with Soo Hyun and that if she wants the insurance, she should ask Soo Hyun about it. Furious, Ok Jeong decides to steal objects from Sun Hee's and opens the money filled briefcase.

One Air team finds out that Eunsung Investment and Securities is interested in investing in their airline. Furthermore, Eunsung has personally invited the team to their Founding Day Event. Woo Jin and Sun Hee cannot be happier and dress up for the occasion. Meanwhile, Tae Yang finds out from Mr. Gong that Tae Ree has set up this meeting between Eunsung and One Air.

Sun Hee and Woo Jin confirm their feelings for each other. They go on their first date at the beach. However, when Sun Hee realises that Woo Jin keeps addressing her as Do Hee, she decides to tell him the truth. Just when she’s about to confess, she gets a call and finds out that Do Hee has woken up.

Tae Ree treats Kang Min like a slave and tells him that the only reason she kept him by her side is because he is smart. Kang Min is humiliated and angry, but he continues to aid her. He plans to put Tae Ree on the very top of Donghae Airlines and then plans to kill her, thus gaining the entire inheritance himself. When he figures out who he will frame for Tae Ree's murder, he will execute his plans immediately.

Woo Jin and Cho Rong see Sun Hee taking the trash out. Woo Jin is shocked to see Do Hee dressed in such comfortable clothes, but Cho Rong covers for her and tells him that it's her mom, Sun Hee. Inside the house, Sun Hee has a difficult time pretending to be Do Hee and often mixed up her role. Meanwhile, Kang Min has found his scapegoat and looks for the right time to take action.

Woo Jin proposes to Sun Hee. She is flabbergasted and does not know how Do Hee would react. She tells him to give her some time to decide. Meanwhile, Do Hee explodes after finding out that she no longer works at Donghae Airlines. Trying to comfort her, Sun Hee tells her that Woo Jin is also a part of One Air.

Do Hee finds out that Woo Jin now has feelings for her. She tells Sun Hee that she'd like to meet him. Sun Hee officially asks Woo Jin out on a date and also demands specific requirements since Do Hee is still not fully well. Since Do Hee can't be out for too long due to her illness, Sun Hee tells Woo Jin that the date shouldn't last too long and that they cannot ride the car.

Do Hee accepts Woo Jin's proposal, and Sun Hee prepares to say goodbye to the crew. While they all have a family dinner, Woo Jin notices that Do Hee is a bit different. He sees her treating Cho Rong cold heartedly. The next day, Woo Jin asks Sun Hee about what kind of house they should live in. Sun Hee does her best to give Do Hee-like answers, but Woo Jin is taken aback.

Chae Kang Min visits Sun Hee's house without any notice. He tells her about Do Hee's threats regarding the slush fund. He also tells her that he has found out that Do Hee has been lying about the fact that she has a twin sister. Sun Hee is told to stop her sister from going any further and to return the money she took. Meanwhile, Sun Hee is kidnapped.

Kang Min orders his men to kidnap Sun Hee. Just when Sun Hee is about to be kidnapped, Woo Jin comes to her rescue. He takes her back home and nurses her until the next morning. She calls his name, and for a second, Woo Jin is confused as to whether she is Sun Hee or Do Hee. Meanwhile, despite the doctor's warning, Do Hee discharges herself from the hospital and goes to work.

Tae Ree comes across Sun Hee and realises that Do Hee has a twin sister. She becomes furious that she did not know about Do Hee’s twin sister and gives orders to find out more about her. Sun Hee decides to start a business with a food truck. Meanwhile, Do Hee and Woo Jin spend the night together.

Do Hee tells Woo Jin that she will try harder to make their relationship work out. However, the subcontractors for Donghae Airlines’ in-flight meals declare a boycott because of the trouble Do Hee caused. Because of the situation, Woo Jin tells Do Hee that only she can prepare the in-flight meal presentation.

Ye Bin starts a one person protest in front of Donghae Airlines as Tae Ree refuses to pay her severance pay. Tae Ree becomes furious and blames Do Hee for everything. She gives orders to bring Do Hee so that she can take matters into her own hands. However, Do Hee claims that she never betrayed Tae Ree.

Sun Hee makes a public announcement as Do Hee. Tae Ree becomes furious once again and gives orders to get her. However, with the help from her many colleagues, Sun Hee successfully escapes. The very next day, Do Hee disbands Airline Flight Attendant’s Union, and many people find it strange for her to suddenly change like that.

Woo Jin asks Do Hee whether Sun Hee has been pretending to be her. Do Hee is shocked, but she pretends to be hurt and understanding. In front of Woo Jin's parents, she tells him that until their wedding, he can do whatever he wants. To make matters worse, she badmouths Sun Hee in front of Woo Jin's mother, saying that ever since Sun Hee's divorce, she has been relying on Woo Jin.

Woo Jin's mother meets Sun Hee. She tells her straightforwardly to stop confusing Woo Jin's feelings and to back off. Meanwhile, Tae Yang visits Sun Hee and presents her with freesias, mentioning that the meaning of the flowers is "a new start". Sun Hee then realizes that it was Tae Yang who brought the same flowers to her before. He also confesses his love for her.

During Do Hee and Woo Jin's wedding, Do Hee is taken to the police station for questioning. Woo Jin suspects that it is because of Donghae Airlines' slush fund and warns Tae Yang to stay out of Tae Ree's mess. Meanwhile, the crew finds out that Tae Ree has been dismissed from her position at the company and fears that she will retaliate.

Tae Ree invites four people to her cottage and plans to murder them by setting the place on fire. Among the four, two of them had tortured her regarding the death of Lieutenant Cha Jong Chul, Sun Hee and Do Hee's late father. The other two are Sun Hee and Do Hee who have also been causing trouble for Tae Ree. However, little does she knows, Kang Min plans to kill his own wife and make it seems like the twins' doing.