Orphaned at young age, abandoned by his uncle and later by his adoptive parents, Sang-doo’s life has been a succession of difficulties. At 27, he makes a living by seducing older women in order to support his daughter’s hospital fee. However, the love he has for his first love, Chae Eun-hwan, keeps him happy and optimistic. When he runs into Eun-hwan again, he decides to give another chance at his love and goes back to high school to be Eun-hwan’s student.

Cha Moo Hyuk is a man who was adopted by an Australian family but treated cruelly and then abandoned at a young age. By chance, he meets Song Eun Chae, a fashion coordinator dedicated to her employer, singer Choi Yune. Their meeting will have implications for the rest of Cha Moo Hyuk's life as a devastating turn of events leads him to delve into his past, and ultimately find happiness.

根据金圣钟推理小说《第五列》改编的8集电视剧，국가를 위협하는 세력에 맞서는 형사의 이야기를 그린 추리드라마