When a mysterious, rapidly spreading viral outbreak plunges Seoul into chaos, a divorced, workaholic fund manager boards the last KTX train to Busan with his young daughter. Aboard the speeding train, the passengers—including a rugged blue-collar worker and a pregnant wife—soon discover they are not alone. As the infected, driven by a insatiable hunger for human flesh, begin to attack, the survivors are forced into a desperate fight for their lives in the confined, hurtling cars. The journey becomes a harrowing test of humanity, sacrifice, and the bonds of family, as the train races toward a rumored safe haven that may not exist.