Monday, September 26, 2016
Seok-Woo, a fund manager who was divorced with his wife earlier, decides to take his daughter Su-an to her mother in Busan as her birthday gift. They board the KTX (a Korean bullet train) at a station in Seoul which is also occupied by the tough working-class husband Sang-hwa and his pregnant wife Seong-kyeong, a high school baseball team, rich but selfish CEO Yon-suk, elderly sisters In-gil and Jon-gil, and a homeless man.
As the train departs, a spasmodic young woman boards the train with a bite wound on her leg and is succumbed. Zombified, she attacks a passing female train attendant who attempted to resuscitate her, and the zombie infection spreads. They infect the baseball team and the other passengers, except Yong-guk, his girlfriend Jin-hee, and two other students fleeing to the front car. News broadcast reports about the zombie outbreak around Korea. The train stops at Daejeon which is seemingly void. While the passengers disembark, they come across the infected military zone and retreat. Zombies break through the room above the train, causing Seong-kyeong, In-gil and the homeless man to separate to the rear train and into the bathroom with Su-an. Realizing the dire situation they are in, the conductor operates the train to Busan, where news of successful decontamination has been heard.
Seok-Woo realized that Su-an was not at her seat. He races with Sang-hwa and Yong-guk to rescue his daughter and others before being chased back by the horde of infected passengers. They manage to reach the front train car, but Yon-suk and the passengers had locked the car door before them, fearing infection. Yong-guk tries to break the front door open while Seok-Woo and Sang-hwa try to block the zombies entering their cabin. However, Sang-hwa is bitten. He tells Seok-Woo to flee and asks him to take care of Seong-kyeong as he begins to transform into a zombie. Just as Yong-guk and Seok-Woo force the door open hindered by stubborn people, In-gil sacrifices herself to buy the others' time to escape to the safe cabin, disheartening Jong-gil.
Outraged, Seok-Woo punches Yon-suk in retaliation, but Yon-suk mistakenly claims that the latter is infected due to splattered blood over his shirt. Yon-suk and the other passengers fearfully demand the escapees to isolate to another car and Jin-hee joins them. Jong-gil realizes that her sister, who is seen almost zombified behind the door, had took her own life for the sake of others' lives, and she angrily sees the selfishness of the other passengers behind her. She thanks her sister and opens the door, letting the zombies rush in and kill the passengers except Yon-suk and an attendant seeking shelter in one of the restrooms. Seok-woo gets a call from one of his employees who said that the outbreak was caused by one of their projects.
Due to a train wreck at East Daegu train station, the survivors are forced to stop. As they try to find another train, they are attacked. Yon-Suk gives the attendant to the zombies to escape. He then throws Jin-Hee to a zombie to save himself. Despondent Yong-guk tries to comfort infected Jin-Hee but is attacked. The conductor who activates the last locomotive saves Yon-suk captured by zombies, but Yon-suk runs to the train, leaving the conductor to be consumed. After the homeless man defends others from zombies to death, Seok-Woo, Su-an and Seong-kyeong successfully board the locomotive. However, Yon-Suk had been inside the engine room in the verge of infection. Seok-Woo fights zombified Yon-suk off, but he is bitten before he throws him off the train.
Not wanting to kill his fellow survivors, Seok-woo pleas Seong-kyeong and Su-an that he needs to let himself go, agonizing his daughter. He commits suicide by falling down the train before he is transformed. Later, Seong-kyeong and Su-an stop at the blocked tunnel's entrance to Busan and walk through it. At the exit, soldiers spot two of them in the tunnel. But since they cannot identify them in the darkness, their commander orders them to shoot. As the soldiers prepare to fire, one of them hears a child singing a song, realizing that both are not zombies but survivors. They rush for the rescue while Su-an tearfully sings.