While a zombie virus breaks out in South Korea, passengers struggle to survive on the train from Seoul to Busan.

Hye-sun has just run away from her former life in a brothel. She now lives with her good-for-nothing boyfriend, Ki-woong, who intends to pimp Hye-sun out again due to money problems. After a fight about this, the two separate and are caught in the chaos bursting out of Seoul Station. Hye-sun escapes with a few survivors into a police station and becomes trapped by a group of zombies within a jail cell, only to realize a surviving policeman in the cell with them has been bitten. Meanwhile, Suk-gyu poses as Hye-sun's father to Ki-woong before interrogating him for Hye-sun's location. The two go to Hye-sun's home, only to find that the landlady had become a zombie.