Yoon-jae goes to an aquarium and sees Yeon-seo sitting on the floor drawing. He’s interested in her. Yeon-seo soon realizes that she has to rush to her job interview. After she grabs her stuff and leaves in a hurry, Yoon-jae finds her portfolio that she left behind. Without her portfolio, Yeon-seo doesn’t get the job. Disappointed, she goes back to the aquarium. Yoon-jae gives her the phone number of his office. Later she goes to his office to pick up her portfolio, but she can’t get it back because of Yoon-jae’s mistake and miscommunication. Meanwhile, when Gyu-eun is working late in the lab, she hears somebody walking down the hall. She thinks that somebody has broken into the lab and she gets nervous. She attacks the intruder in the dark with a fire extinguisher. However, it’s Yoon-jae who comes to look around the building he has designed. Later, both Yeon-seo and Gyu-eun talk about a strange, but interesting encounter with an attractive man.
Yeon-seo is happy to find out that she got the job at Yoon-jae’s office. She wants to share the news with Gyu-eun and hurries to her lab. There she finds Gyu-eun and Yoon-jae together. Yeon-seo realizes that Gyu-eun really likes Yoon-jae. She decides to hide her feelings. Soo-hyeong, who has been away for his volunteer work, comes back. Gyu-eun tells him to take good care of Yeon-seo if he likes her. Meanwhile, Gyu-eun and Yoon-jae have a great time together and their love grows. They decide to get married. Yeon-seo receives a wedding invitation, which makes her depressed. Soo-hyeong tries to make her feel better.
Gyu-eun undergoes a surgery. Yeon-seo nervously waits outside. Gyu-eun is still unconscious even several days after the surgery. Yoon-jae is shocked to hear from the doctor that Gyu-eun is in a coma. He comes back home, and his pictures from the honeymoon are delivered. He bursts into tears. Without knowing how long Gyu-eun will be in a coma, Yoon-jae decides to move her to their house. Yoon-jae’s parents try to persuade him not to legalize the marriage, but he insists. Soo-hyeong is curious about the person Yeon-seo likes. He asks Yoon-jae if he knows anyone in the habitat project group that Yeon-seo has in mind. Yoon-jae realizes that Yeon-seo likes him.
Soo-hyeong comes to Yeon-seo’s office to see her. They go to the elementary school they used to attend together. There Soo-hyeong gives Yeon-seo a ring. Meanwhile, Yoon-jae feels a little bit jealous when Soo-hyeong goes out with Yeon-seo. Both Yoon-jae and Yeon-seo realize that they have special feelings for each other. Scared, Yeon-seo decides to quit her job and leave the country. Three years later, Yoon-jae builds a new house and moves in with Gyu-eun. Yeon-seo comes back to Korea from Australia. Soo-hyeong goes to the airport to pick her up.
During an important presentation, Yoon-jae receives a call from a nurse that Gyu-eun’s condition is critical. He discontinues his presentation and hurries to the hospital, which jeopardizes his company. Yoon-jae’s professional and personal life get out of shape. Yoon-jae and Yeon-seo have an argument over Gyu-eun. Later, they make up with each other. Yeon-seo realizes that she’s more and more attracted to Yoon-jae. However, she tries to be more interested in Soo-hyeong. Gyu-eun has to stay in the emergency room for a couple of days. Exhausted emotionally and physically, Yoon-jae stares at Gyu-eun’s oxygen tube and life support equipment as if he has made up his mind.
Yeon-seo visits Gyu-eun in the hospital and happens to see Yoon-jae trying to unplug Gyu-eun’s life support system. Yeon-seo tries to stop him and comfort him. Yoon-jae hugs her tight. Yoon-jae and Yeon-seo feel uncomfortable when they run into each other at work. Meanwhile, Soo-hyeong plans to get married with Yeon-seo. Without knowing that Yeon-seo likes Yoon-jae, Soo-hyeong invites both of them to dinner. Yeon-seo and Yoon-jae don’t know how to act around Soo-hyeong. Yeon-seo loves Yoon-jae, but she feels terribly guilty when she thinks of Gyu-eun. After giving it a lot of thought, Yeon-seo decides not to see Yoon-jae anymore.
Soo-hyeong can’t believe his eyes when he sees Yoon-jae and Yeon-seo together. Furious, Soo-hyeong punches Yoon-jae in the face and walks away. Yoon-jae and Yeon-seo feel miserable about their situation. Realizing that Soo-hyeong can’t forget Yeon-seo, Yoon-hee decides to meet Yeon-seo. Meanwhile, Gyu-eun who has been in a coma moves her hand. Her family members get excited, but then are disappointed when they find out that her condition didn’t get any better. After giving it a lot of thought, Yoon-jae decides to keep his distance from Yeon-seo. He tells her not to see him.
Yeon-seo asks Yoon-jae to leave with her. Feeling guilty and scared, the two drive away with no definite destination. Meanwhile, everyone is worried when Yoon-jae and Yeon-seo don’t show up at work. Yeon-seo and Yoon-jae arrive at a small village by the ocean and find a place to live. Yeon-seo is just happy to be with Yoon-jae. However, after they disappear, Gyu-eun comes out of the coma. Her family can’t believe the fact that Gyu-eun wakes up as soon as Yoon-jae leaves her.
Gyu-eun asks about Yoon-jae, but her family doesn’t dare to tell her the truth. Gyu-eun leaves the hospital and goes home. She’s very touched to see the house that Yoon-jae has built for her. Yeon-seo hears about Gyu-eun and tells Yoon-jae. He has been excited about starting a new life with Yeon-seo, but he’s terribly confused by the news. Yeon-seo realizes that she has to let him go. Yoon-jae can’t help but cry when he sees Gyu-eun greeting him with a big smile. Feeling guilty, Yeon-seo can’t go see Gyu-eun. She finds Soo-hyeong waiting for her in front of her house. She feels sorry for him.
To make up for the time she spent in the hospital, Gyu-eun is eager to get back to normal. She realizes that Yoon-jae celebrated their wedding anniversary while she was in a coma. She feels grateful and also sorry for him. However, Yoon-jae’s heart aches whenever he thinks of Yeon-seo. Meanwhile, Yeon-seo focuses on her work and keeps herself busy to forget about everything. Without knowing what happened between Yoon-jae and Yeon-seo, Gyu-eun can’t understand why her best friend doesn’t come to see her more often. Gyu-eun insists that the three of them go on a picnic together. Yeon-seo and Yoon-jae feel awkward. Soo-hyeong tells Yeon-seo that he’ll be there for her when she needs someone to rely on. However, Yeon-seo tells him that she doesn’t deserve his favor. All of a sudden, she feels a terrible pain in her stomach and collapses.
Yoon-jae is shocked to hear from Soo-hyeong that Yeon-seo is pregnant. Meanwhile, Gyu-eun doesn’t feel comfortable since she notices that Yoon-jae is hiding something from her. Gyu-eun happens to find out that Yeon-seo is pregnant, but she doesn’t know that the baby is Yoon-jae’s. She’s supportive about Yeon-seo’s decision to have an abortion. Yeon-seo can’t tell Gyu-eun the truth. Yoon-jae comes to see Yeon-seo at her work, but she avoids him.
Gyu-eun is extremely bothered about the fact that Yoon-jae is hiding something from her. She talks to Soo-hyeong, who knows everything. However, Soo-hyeong doesn’t tell her the truth. Yeon-seo goes to the clinic to have an abortion, but at the last minute she changes her mind and decides to keep the baby. At home, she listens to the cassette tape that she recorded with Yoon-jae while they stayed on the island. Worried about Yeon-seo’s being depressed, Gyu-eun prepares a surprise birthday party. Yoon-jae and Soo-hyeong are invited to Yeon-seo’s house. While preparing the party, Gyu-eun happens to find something that finally tells her what has happened between her husband and her best friend.
Gyu-eun is shocked to listen to Yeon-seo and Yoon-jae’s recorded conversation. She still can’t believe that her best friend and her husband are having an affair. She tells Yeon-seo that she must have heard wrong, but Yeon-seo bursts into tears. Gyu-eun storms out of the house. Yoon-jae feels miserable. After staying up all night, Gyu-eun packs up her stuff and leaves the house. Yoon-jae tries to stop her by telling her that he’s sorry, but Gyu-eun doesn’t even look him in the face. Yoon-jae tells her that Yeon-seo was the only person that gave him hope. However, Gyu-eun can’t stand him talking about another woman. Having no place to go, Gyu-eun goes to Soo-hyeong.
Gyu-eun asks Yeon-seo if she loves Yoon-jae. When Yeon-seo says no, Gyu-eun tells her not to see Yoon-jae again. She also tells Yeon-seo that she’ll only remember their good days as best friends. Gyu-eun tries to keep her cool, but she’s heartbroken. Yeon-seo decides to quit her job and go back to her hometown where her mother lives. Gyu-eun and Yoon-jae try to go back to normal. However, Yoon-jae sometimes seems absent-minded, which drives Gyu-eun crazy. Gyu-eun hears from Soo-hyeong that Yeon-seo has left the town. She feels bad about Yeon-seo. Meanwhile, Yeon-seo hasn’t told her mother about her pregnancy. She’s worried about making a living with a baby.
Gyu-eun comes to see Yeon-seo. Yeon-seo is worried about what Gyu-eun is going to tell her. Gyu-eun tells her to stop making situations where she has to meet Yoon-jae in person. Feeling miserable and shocked, Yeon-seo collapses. Gyu-eun takes her to the hospital. Gyu-eun is heartbroken and feels guilty when she finds out that Yeon-seo has lost her baby. She decides to tell Yoon-jae. Meanwhile, Soo-hyeong tells Yeon-seo that he wants to start a new life with her. However, Yeon-seo refuses, telling him that he knows too much about her. However, Soo-hyeong doesn’t want to give up.
After leaving the hospital, Yeon-seo goes to the house where she used to live with Yoon-jae. Without knowing what’s going on, her old neighbor wonders why she came alone without Yoon-jae. Yoon-jae looks for Yeon-seo. Soo-hyeong asks Gyu-eun if she knows where Yeon-seo might be. However, Gyu-eun stuns him by saying that Yeon-seo will never call her again. Finally, Yoon-jae finds Yeon-seo at their old house. Yoon-jae tells her that he’s terribly sorry about the baby. She leaves Yoon-jae behind and disappears again. Gyu-eun and Yoon-jae get divorced. They feel sad about the fact that it takes only a few minutes for them to become legally strangers.