Cha Yo-Han—an arrogant but genius doctor of anesthesiology—and Kang Shi-Young—a smart, warm resident of anesthesiology—work together to help people with mysterious cases of acute or chronic pain.
Lee Young-Joon's family runs a large company and he works as the vice-president of the company. He is smart, rich and handsome, but he is arrogant. His secretary is Kim Mi-So. She has worked for him for years and she is perfect for him, but Kim Mi-So decides to quit her job.
Go Ho is a 29-year-old advertisement contractor who wants success in both her career and romance. Unfortunately, neither seems to be working out particularly well because the only two men in her life are Kang Tae Ho, her short-tempered boss, and Hwang Ji Hoon, her ex-boyfriend. Dealing with their increasingly irritating behavior and her decreasingly abundant time until she hits the “big thirty,” can Go Ho reach for the skies and capture her dreams, or will this starry night end in darkness?
Jo Jin-Gab was once a promising judo athlete. He protested against corruption at a game and he was kicked out of the sport. After that, Jo Jin-Gab became a gym teacher. Again, he could not control his anger against the son of the school's chairman. Jo Jin-Gab was once again kicked out of his profession.
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.
Nam Se-Hee is a single man in his early 30s. He has chosen to not marry. He owns his home, but he owes a lot on his mortgage. Yoon Ji-Ho is a single woman in her early 30s. She does not own a home and envies those that do. She has given up on dating due to her financial struggles. Yoon Ji-Ho begins to live at Nam Se-Hee’s house. They become housemates.
Seo Jae-won who suffered an unfortunate childhood, becomes an ambitious and driven CEO that chases after success. But when her obsession gets out of hand, she tries to escape from her unhealthy desires but her husband, a designer and college professor, gets swept up in the process.
