In Seoul, South Korea, securities company manager Seo Seok-woo, neglecting his daughter Soo-an after his divorce, takes her to Busan to visit her mother on her birthday, boarding the KTX high-speed train from Seoul to Busan. However, a mysterious virus begins to spread throughout the country, turning all infected individuals into bloodthirsty zombies who then spread the virus to more citizens through biting. The government, mistaking it for a riot, sends in the army to quell the unrest, which only causes the infection rate to surge. A woman bitten on the leg by a zombie escapes onto the train Seok-woo and Soo-an are on for refuge, subsequently turning into a zombie and attacking the train crew and other passengers.