Train

Detective Do-won has feelings for prosecutor Seo-kyung, but after hearing about her past, he begins to ignore her; while Do-won is chasing after a suspect of a case, he faces another case of murder at Mugyoung station.

While investigating the fifth victim of the case of murder at Mugyoung station, Do-won senses something odd and something unexpected occurs.

Do-won discovers clues, but they all seem to be irrelevant to the case; he runs back to Mugyoung station, where he faces an entirely new world.

Do-won meets Seo-kyung apart from the present world and realizes that he also exists in that world; unlike the present world, Do-won is being chased for murdering Jin-sung.

Do-won realizes that he, in the present world, exists for Do-won in the other world; as he straightens out the mixed-up situation, he finds out about the truth behind the death of Seo-kyung's father.