Train

Do Won and Seo Kyung both lose their fathers on the same night 12 years ago. In the present day, Do Won is a police officer and Seo Kyung a prosecutor. The police discover several skeletons on the train tracks at Mukyeong Station, which has been closed for five years. Do Won heads to the station while chasing a key suspect.

Do Won confesses to Seo Kyung that his father was the one who killed Seo Kyung’s dad 12 years ago. Seo Kyung feels shocked and betrayed. Meanwhile, Do Won chases the suspect of the Mukyeong Station Serial Murders, and Seo Kyung discovers her mother’s stolen jewellery from 12 years ago on the recently discovered corpses.

Seo Kyung dies at the hands of the Mukyeong Serial Killer. Do Won realizes that this is the same culprit from the murder case 12 years ago. However, the more he investigates, the more mysterious things seem to get. Just as he is falling deeper into sorrow over losing Seo Kyung, Do Won sees someone at Mukyeong Station.

Do Won arrives in World B and meets the Seo Kyung of this world. The other Do Won is supposedly on the run after being named a prime suspect of the murder of a drug broker. He is confused about whether or not the other Do Won really is the culprit. Meanwhile, he is shocked to meet someone unexpected in this world.

The Seo Kyung of World B transfers to Mukyeong Police Station. Do Won of World A starts his search for the victims of his last case before coming to World B, the Mukyeong Station Serial Murder. Meanwhile, a new missing person case comes into Mukyeong Police Station, and Do Won runs into an unexpected person while chasing down a key suspect.

Jin Woo is the prime suspect in World B, and Do Won tries to figure out what has happened in this world. Seo Kyung seems to have a dark past in World B. Do Won tries to console Seo Kyung, but she doesn’t want Do Won to get closer. Jin Woo in World B did not have Do Won to stop him from his wrongdoings.