Lee Sang-won is policeman and a single parent. He is anything but reliable, but he deeply loves and cares about his teenage daughter Jeong-hyeon. One day Jeong-hyeon gets a new teacher called Cheol-woong and the young falls in love with him. Cheol-woong knows its wrong, but eventually can’t resist her anymore. Her romance must be kept as a secret, but as Sang-won fails sometimes to be a father, as sharp and clever he is as a cop. He discovers the love affair and confronts Cheol-woong violently, though Jeong-hyeon pleads him to stop. But Sang-won feels that something must be wrong with the teacher and takes a closer look at his past. To Sang-won’s surprise he find’s a trace to an unsolved murder case he investigated 10 years ago, which sets his mind on fire. What if Jeong-hyeon is dating a murderer?