Gong Woo-jin is a 30-year-old single man who works as a set designer. Due to a trauma he experienced 13 years ago, he does not want to have a relationship with others. When Woo Seo-ri,
was 17, she fell into a coma. Thirteen years later, she wakes up from her coma, but she is now 30-years-old. Gong Woo-jin and Woo Seo-ri get involved with each other and fall in love.
Gong Woo-jin caused an accident when he was 17 years old, or so he believes. Due to the crush he had on a girl of his age, he caused her to stay on the bus she was travelling for one stop longer than required. As a result, she was still on the bus when it crashed, and later Gong Woo-jin finds out that this girl (No Soo-mi) died in the accident. He feels very guilty and goes away to study in Germany, and carries this guilt with him into adulthood. As a result, he becomes a very strange adult. His habits include getting out a tape to make measurements for his set design miniatures at any given moment. He often gets into trouble for this habit, and he's also cold and rude to others. He even leaves Korea for long periods of time to go on trips without a word to anyone.
Woo Seo-ri wakes up in hospital confused to find that she has aged 13 years overnight. She last remembers being 17 years old, wearing her friend No Soo-mi's jacket since she forgot to pick up her own. She was in a coma, and woke up after 13 years to find herself much older and very weak. Sadly, she has no visitors, and the staff can't even find out where her relatives (her Aunt and Uncle; her parents died when she was young) are. Seo-ri finds this out after overhearing the nurse who keeps fobbing her off with excuses talking about how they say this to patients whose relatives don't come by anymore.
She decides to take matters into her own hands and search for her Aunt and Uncle. She goes to the last place she remembers them - their home - but the city is hugely changed from how she remembers. By a twist of fate, her Aunt and Uncle no longer live there: they sold the house to Woo-jin's father, who is now letting his adult son stay there while he's back in Korea. Woo-jin is also looking after his nephew, Yoo Chan, an energetic and friendly guy who instantly wants to take care of Seo-ri, despite Woo-jin's misgivings. Neither of them recognize one another at first, but Woo-jin agrees to let her stay for just one night so that she can begin the search for her relatives.
Meanwhile, at the hospital, a doctor is dismayed to hear that Seo-ri has gone missing and begins to search for her. The next day, he asks about her at her old home - but a misunderstanding doesn't let them meet.
