Sok-woo, a father with not much time for his daughter, Soo-ahn, are boarding the KTX, a fast train that shall bring them from Seoul to Busan. But during their journey, the apocalypse begins, and most of the earth's population becomes flesh-craving zombies. While the KTX is shooting towards Busan, the passengers fight for their families and lives against the zombies—and each other.