Born with a weak heart, Hye Won is envious of her school friends being able to run freely. Suddenly, she collapses in the rain. Meanwhile, Min Woo, a college student, runs for cover in the rain and encounters Eun Hye. Unfortunately, Eun Hye dies on the day of her wedding to Min Woo. Fast forward many years, and Hye Won is living as a florist. She and her friend, Jang Mi, visit the mountains to collect wildflowers. Hye Won gets separated from Jang Mi and becomes lost in the woods.

Min Woo and Hye Won meet in the mountains. Min Woo is attracted to Hye Won who is a lot like Eun Hye. Hye Won's heart flutters fast when she's with Min Woo. The two end up spending the night together in a hut, and Hye Won gets her leg injured while coming down the mountain. Worried, Jang Mi calls up Hye Won's fiance Jung Jae, who rushes over. At the foot of the mountain, the three of them meet.

Min Woo and Hye Won run into each other in a tea field and are surprised by the coincidence. It's almost as if Hye Won had been there before. They rush to catch a bus and barely make it to the train station on time, but the tickets are sold out. Min Woo offers his train ticket to Hye Won. Hye Won falls asleep on the train, and wakes up to see Min Woo in front of her. When they arrive in Seoul, Hye Won offers Min Woo her business card, before she catches a glimpse of Jung Jae waving at her.

The four visit Min Woo's favorite field of wildflowers. Jung Ah catches Min Woo and Hye Won together and mistakenly thinks they are kissing. Jung Ah, unable to contain herself, lashes out at the two, only to find out that it was a misunderstanding. Min Woo and Hye Won are teamed up for a renovation project. Min Woo asks Hye Won to be his date for the opera. Hye Won hesitates at first, but agrees to go as a friend. Jung Jae also gets tickets to the opera for Hye Won.

The four arrive at Calla Resort. Jang Mi and Dae Pung frequently argue, but Min Woo and Hye Won always voice singular opinions. Jung Jae tells Min Woo that he should forget his former flame and pursue a new love interest. Meanwhile, Min Woo's feelings for Hye Won grow stronger. Jung Ah finds the two taking photos and expresses discomfort about the fact that she had seen them nearly kissing. After the misunderstanding is cleared up, the four people enjoy a cheerful time at the lake.

Hye Won finds out how Min Woo truly feels about her. In order to push Min Woo away, she tells him that she's already part of Jung Jae's family. She also tries being cold to Min Woo, and tells him that she doesn't even want to be friends. Min Woo perceives that Hye Won is angry, and tries to cheer her up, to no avail. The shop owners at the mall start to develop ill feelings towards Jung Jae. Min Woo feels sorry for the business owners, but Hye Won sides with Jung Jae on the matter.

Jung Jae visits Hye Won, who is working on the \"Proposal Room.\" He sees Hye Won warming up to Min Woo and feels left out. Jung Jae proposes to Hye Won in the room, but Hye Won turns him down. Meanwhile, Jung Ah discovers a necklace in Min Woo's room, only to get upset when she finds out that Hye Won already knows about the necklace. Jung Jae discovers that his necklace is missing, and searches for it. Hye Won forgoes an appointment with Jung Jae to help find the necklace.

Hye Won passes out at her engagement ceremony and Jung Jae becomes very concerned. Min Woo finds out from Jang Mi that Hye Won has had a heart transplant. Min Woo rushes to Hye Won's side at the hospital. Meanwhile, Hye Won is in a coma when she dreams about a strange man calling out for her. Min Woo looks on as Hye Won is comforted by the mysterious voice. He leaves behind a picture he drew of Hye Won. When Hye Won wakes up, she finds Jung Jae watching her anxiously.

Jung Jae discovers Min Woo and Hye Won spending together at a park, and decides he must take action. Jung Jae visits Min Woo and asks him to forget about Hye Won. Min Woo is hurt but decides to stop having feelings for her. Meanwhile, Min Woo tries not to be alone with Hye Won. When Jung Jae becomes able to confirm that Min Woo is no longer pursuing Hye Won, he is relieved. Min Woo tries to be cold to Hye Won on the job. Hye Won meets Min Woo at the folk dance event Jung Ah has organized.

Jung Jae and Jung Ah become worried when Hye Won doesn't return from a trip she took alone to an island. Min Woo gets concerned and rents a motorboat to go after Hye Won, only to find her acting cold toward him. Despite such a demeanor, Hye Won is actually grateful and happy to see Min Woo. Jung Jae is nervous about Min Woo and Hye Won, but he is relieved to hear from Dae Pung that Min Woo has returned to the resort. Min Woo secretly finds a place for Hye Won to stay at.

When Jung Jae sees Hye Won getting off the boat, he tries to stay calm. But Jung Ah gets angry and tells Hye Won she won't forgive her. Meanwhile, Dae Pung updates Min Woo on what had happened and advises him not to do anything to worsen the situation. Min Woo tries to protect Hye Won, but Jung Jae gets enraged and punches him. Meanwhile, Jung Ah asks Hye Won to break up with her brother. Hye Won, feeling guilty, tries to break up with Jung Jae, but he refuses to.

When Min Woo hears how Hye Won has left home alone, he takes Dae Pung's car in search of her. Jung Jae, desperately waiting for Hye Won, asks Jang Mi to call him if Hye Won returns home. Jung Jae returns to the resort to focus on renovation efforts, only to be hurt when he hears Jung Ah mention Hye Won may be with Min Woo. Eun Hye's Dad comes to meet Jung Jae at the resort to ask that his wife wishes to meet the recipient of Eun Hye's heart, but Jung Jae turns him away.

Hye Won runs away from the summer home and hops into Min Woo's car. Jung Ah cleans up Jung Jae's mess, only to discover Eun Hye's Dad's message with \"So Eun Hye\" written on it. When Jung Jae realizes that Hye Won's heart donor is Min Woo's first love, he rushes to the hospital to get confirmed facts. Jung Jae meets Eun Hye's Dad and asks that he doesn't look for Hye Won. When Min Woo doesn't take her calls, Jung Ah calls Min Woo's Mom and discovers that he will be going to the flower field.

Hye Won comes across Eun Hye's grave. The former thanks the latter for donating her heart. Min Woo watches this from afar and gets saddened. Hye Won tells Eun Hye's Dad that she'll come to visit him from time to time, but Eun Hye's Dad insists that's not necessary. Later, Min Woo visits Eun Hye's home, and Eun Hye's Mom asks Min Woo if he had forgotten all about her daughter. Min Woo is so sad that he spends the night awake in Eun Hye's room.

Jung Jae tells Min Woo that Min Woo's heart is directed toward Eun Hye, not Hye Won. Jung Jae says that the act of telling Hye Won about Eun Hye would actually help her. But Min Woo is worried about Hye Won's heart condition. He promises not to attend his own commitment ceremony in exchange for keeping things a secret. Meanwhile, Jung Ah finds out the identity of the heart donor. Jung Jae asks her not to tell Hye Won, but Jung Ah is too consumed by anger to be considerate of her friend.

Hye Won finds out from Jung Ah that the heart donor was a woman. Hye Won calls Eun Hye's Dad and leaves a voice mail. Hye Won asks Jung Jae whether the heart donor was female, and wonders why he didn't tell her before. Eun Hye's Dad meets with Jung Jae and tells him that since Hye Won knows the truth, he could tell her about Eun Hye's heart. But Jung Jae stresses that Eun Hye's dad must never tell Hye Won the truth because Min Woo and Hye Won are in love.

Hye Won finally finds out about the secret surrounding her heart donor but finds herself unable to retract her feelings for Min Woo. Eun Hye's Dad tells Min Woo to share his heart with Hye Won. Min Woo tells him that he'll be happy with Hye Won and do his part to live on behalf of Eun Hye. Hye Won tries to avoid Min Woo, but ends up meeting him in an awkward situation.

Hye Won tells Min Woo that they must break up, but Min Woo is unable to believe her decision is a genuine one. Hye Won refuses to be overshadowed by Eun Hye. Jung Ah is glad that Hye Won found out about her heart donor, but does not alert Min Woo of the fact. Jung Jae is upset when thinking about how hurt Hye Won would've been when she found out the truth. After a medical checkup, the doctor asks Jung Jae whether Hye Won had recently experienced a shock that worsened her heart condition.

When Min Woo finds out Hye Won is already aware that Eun Hye had donated her heart, he is taken aback. Min Woo rushes to talk to Hye Won, but Hye Won treats him coldly. Unwilling to take Eun Hye's place, Hye Won fights back her feelings for Min Woo. Jung Jae finds out that Min Woo had come to visit Hye Won, and is worried that Hye Won may waver. However, Hye Won declares to Jung Jae that the person Min Woo loves is Eun Hye. Meanwhile, Min Woo comes across Hye Won's wedding invitation by chance.

Min Woo waits for Hye Won at the wedding venue, only to find out from Jang Mi that Hye Won has passed out. Shocked, Jung Jae rushes to the hospital, only to find Min Woo already waiting there. Jung Jae grabs Min Woo by the collar and blames him for everything that has happened. The doctor tells Jung Jae that Hye Won is in critical condition. While everyone waits for Hye Won to gain consciousness, Jung Jae tells Min Woo to leave.