Having married young, when frustration with their lives make Choi Ban-du and Ma Jin-joo regret their marriage of 18 years, a strange occurrence has them traveling back in time to the day before they met and into their younger selves.
Park Jung-Woo is a prosecutor at Seoul Central District Prosecutors' Office. One day, he wakes up and finds himself in locked up at the police station. He has temporary amnesia. Park Jung-Woo is falsely accused and is sentenced to death. He must struggle to prove his innocence.
Kim Seo-Jin is a man who is driven only to achieve success in his life. Thanks to his efforts, he is the youngest executive at his company. His life is perfect, with his beautiful violinist wife Kang Hyun-Chae and a daughter. His wonderful life comes to a halt when his young daughter is kidnapped. He falls deep into despair. To change the past, when his daughter was kidnapped, he contacts Han Ae-Ri approximately one month in the past.
Han Ae-Ri has busy days with her studies and working a part-time job to make enough money to pay for her sick mother's operation. One day, her mother suddenly goes missing. Han Ae-Ri falls into despair, when Kim Seo-Jin from the future contacts her.
When they were children, Yoon Na Moo and Gil Nak Won were each others first love. They are forced to break apart when Na Moo's father Yoon Hee Jae, a psychopath serial killer, murders Nak Won's parents. 9 years later Yoon Na Moo is known as Chae Do Jin, a passionate and kind rookie detective wishing to atone for his father's sins. And Gil Nak Won is now Han Jae Yi, an aspiring actress following in the footsteps of her mother. She suffers from a panic disorder but still has a good outlook on life. However, the sadness of their past comes to light again and their short-lived encounter is over before it began. Another three years on, Jae Yi has become a popular actress and Do Jin is now an experienced detective. When their fate becomes connected once more, will their love prove to be stronger than their past?
Choi Kang-Woo is a former detective, but he now works as a veteran insurance investigator. He leads a team that attempts to reveal insurance fraud cases.
Chef Seo Poong was once a star chef and worked at the best Chinese restaurant. His popularity faded and he eventually wound up working at a small, failing Chinese restaurant. Meanwhile, Doo Chil-Seong is the owner of a building. He is an ex-gang member and he was in jail for 5 yers.
Go Nam-soon, a young boy, constantly gets bullied by a group in his class. Later, one of his old rivals joins his school. Eventually, they are able to sort out their differences.
18-year-old Kang Gyung-Joon's spirit suddenly becomes transplanted in the body of 30-year-old Seo Yoon Jae. Seo-Yon-Jae is a successful doctor and engaged to high school teacher Gil Da-Ran. Gil Da-Ran just so happens to be the teacher of 18-year old Kang Gyung-Joon. More problems ensue when 30-year-old Seo Yoon Jae falls in love with another woman.
A woman with a gift for lying is employed by a chaebol heir to act as his long-lost cousin. To keep up the charade for his family, the two must live under the same roof, but their growing attraction to each other poses a problem for pretending to be relatives.
Yun Hae Jun is the youngest anchor to ever work at his broadcasting station. He is calm and straightforward as a journalist and kind in his personal life. On the other hand, Baek Yun Yeong dreamed of becoming a writer but wound up working at a publishing company.
The two somehow travel back in time to the year 1987. There, Yun Hae Jun tries to find the truth behind a serial murder case, while Baek Yun Yeong attempts to prevent her parents from marrying. They soon realize that their objectives are connected.