(After spending a short amount of time 2001, the film uses a non-linear structure through extensive use of flashbacks and timeskips of indeterminate duration, including flashbacks within flashbacks. However, each of the sequences, 2001 and 1996, occur roughly in order.)
Summer of 1996
Ji-hwan is an amateur photographer working part-time at his older friend's cafe. Two young women enter and when they leave Ji-hwan chases after them, declaring his love for Soo-in. Soo-in feels uncomfortable and Ji-hwan leaves only to shortly return holding a clock over his face with a note saying he has wound back time so that in the future they can meet again as friends as if his declaration of love never happened.
The girls turn up at his workplace unannounced and they bond. After Ji-hwan stands up for Soo-in against two men disturbing her at the movie, all three quote a line from the movie
"I'm in love. It hurts but I want it to go on hurting." with both the girls appearing to be developing feelings for Ji-hwan.
Soo-in enlists Ji-hwan's help in dating the guy who works at a manhwa store only she later tells Ji-hwan she has changed her mind as the man is insincere. (However, near the end of the film the guy is seen re-reading a note she wrote to him and he has a photo of her taped to his army bunk.) The trio take a magazine personality test and unseen by either of the other two, Gyung-hee is secretly happy when her personality and Ji-hwan's are seen as a good match. However, the cafe owner comes along and says how lucky the other two to have found love, a sentiment that hurts Gyung-hee. Gyung-hee and Soo-in fight which confuses Soo-in. They soon reconcile and runaway to go on a road trip, asking Ji-hwan along.
During the trip, Soo-in watches Ji-hwan sleep and caresses a mole on his ear. In the morning she is absent and Ji-hwan nearly kisses a sleeping Gyung-hee. Going outside he asks Soo-in about her first love. She says it was a young boy at hospital when she was a young girl. They both spent a long time there but he never complained and kept her spirits up. She told the boy they would swap names so that even if they separated they would still be connected. Admiring the scenery in the rain trio promise to return in winter. Soo-in becomes ill due to the rain. While she rests alone in a hotel room, Gyung-hee cries, scolds Ji-hwan for being disturbed by seeing her cry (she is normally cheerful) and then she leans in and kisses him.
After returning to Seoul, Soo-in is still ill and the other two go out with Ji-hwan commenting it's like a date. Gyung-hee becomes uncomfortable, insists they change plans and go drinking, then scolds Ji-hwan for acting like her boyfriend when he isn't. She storms off.
Later, the girls attend a party at Ji-hwan's work. Ji-hwan comments that it is taking forever for her to get over her cold. Soo-in sings a love song about the three of them and then leaves early, asking Ji-hwan to walk with her. She touches his face to remember it. Before Gyung-hee leaves, Ji-hwan writes a note addressed to Soo-in declaring his love for Gyung-hee. He expects Gyung-hee to read it and includes lines written to her. He gives it to Gyung-hee to give to Soo-in. Thinking it is a love letter to Soo-in, when he has gone Gyung-hee starts to open it but then tears it up.
Some time later, Gyung-hee visits Soo-in in the intensive care unit. Soo-in reads aloud a letter that she wrote to Gyung-hee. She says she has been brave while receiving treatment and that she was expecting Gyung-hee and Ji-hwan to come to her as a couple. It gets too much for Gyung-hee who says she'll read it later. Soo-in gives Gyung-hee awax sealed
letter to be given to Ji-hwan.
Late Autumn of winter 1996
Ji-hwan has not seen his friends for months and he is chided by his boss for not getting their addresses or phone numbers despite all the time they spent together. Ji-hwan receives a phone call and meets Gyung-hee for a drink. He immediately asks about her injured right hand which she dismisses as just an injury. When he asks about Soo-in she tells him they became uncomfortable around him, he says the same about them, and tells her to go if she has nothing else to say. She leaves, he stays and gets drunk. When he leaves he falls down, punches the ground in anger and falls asleep. He awakes in his bedroom with his hand bandaged. (A brief flashback occurring later shows Gyung-hee tending to his injury in his bedroom while he is asleep, kissing him, then leaving.)
Ji-hwan opens yet another handmade envelope containing only a black and white photo with no sender information on or in the envelope. He visits his former workplace, a cafe, where his friend the owner returns to him a box of photographs. Ji-hwan decides to track down his former friends, Gyung-hee and Soo-in, two young women whom he has not seen for five years. Going to their high school, a teacher who was their classmate tells him that both girls missed a lot of school as they were very sick. She says Gyung-hee died five years ago and Soo-in left Seoul after that.
Ji-hwan goes to the small town where the envelopes are postmarked but the postman denies any knowledge of the sender. (However, in a brief flashback the postman is seen to sneak into a woman's house and take one of the envelopes from under her bed. In voiceover, the postman says he is in love with the woman, that he wonders why she has a suitcase full of the letters, and that he will deliver the letter because he's a postman.) Walking around the town Ji-hwan hears children calling his name, only to find it is the name of their dog. A neighbour of the woman from whose house the envelopes are taken from tells her they have found Ji-hwan. The woman goes out expecting to see her dog but instead she is greeted by her former friend and Ji-hwan sees that Gyung-hee is still alive, albeit not looking as vibrant as she did five years ago. They touch faces as Soo-in had touched Ji-hwan's face when they last met.
After The Wedding
Alone, Ji-hwan opens another envelope. It contains the sealed letter Soo-in wrote on her deathbed, saying she thinks she will be dying soon and giving him advice on how to date Gyung-hee.(In the flashback showing the letter being written, Soo-in draws a mark on her father's ear to match Ji-hwan's so that her dad will look more handsome.) The envelope also contains a letter from Gyung-hee. She confesses that she tore up his letter to Soo-in. She thanks him for his kindness and for passing on the love of photography to her. She thanks him for accepting her awkward kiss a long time ago. Then she says that she has been feeling very weak and has told her dad about what she wants at her funeral, including her beloved Ji-hwan. The camera pans to the beautiful blue sky, her voiceover says that she will be seeing Soo-in soon. "Goodbye Ji-hwan. I loved you before and I love you now. Goodbye."
The last shot is the trio in happier times, a photo taken on their road trip.
She accompanies Ji-hwan to the wedding of the cafe owner where they make a wonderful couple.