The mind of 18 year old Kang Kyung Joon somehow gets trapped in the body of 30 year old Seo Yoon Jae, who just happens to be Kyung Joon's future brother-in-law.
"You Who Rolled In Unexpectedly"tells the story of TV drama director Hong Yoon-Hee and surgeon Bang Gwi-Nam after they get married ... Yoon-Hee (Kim Nam-Joo) is a TV drama director. She recently married the perfect man for her. Yoon-Hee has been afraid of having in-laws, specifically a mother-in-law. Because of this, Yoon-Hee looked for a guy who isn't closely connected to his family. If she couldn't find such a guy, Yoon-Hee planned on staying single. Finally, Yoon-Hee met Terry (Yu Jun-Sang). Terry is a doctor with a sweet personality, but, most importantly, he has adopted parents from America. Terry has no recollections of his real parents and was adopted by the Korean couple in America as a young child.