Han Jung-seok, Gang Dong-won leads a tense evacuation as a zombie outbreak sweeps South Korea, forcing international help and a quarantine that locks down the peninsula in Busan. He drives his sister, Min-jung, her husband, Chul-min Kim Do-yoon, and their young son, Dong-hwan Moon Woo-jin, toward a waiting ship. The group encounters a distressed couple with a young daughter begging for a ride, but Jung-seok refuses after spotting the husband’s bleeding wound. Onboard, an infected passenger turns and bites several people, including Dong-hwan. Min-jung is bitten while staying behind with her son; Jung-seok seals the cabin to contain the outbreak, preventing Chul-min from entering as armed soldiers intervene.
Four years later in Hong Kong, Jung-seok, Chul-min, and two other Korean refugees are drawn back to the peninsula by Chinese mobsters who want them to recover a truck carrying US$20 million. The deal promises them half the money. The team locates the truck at night and shoots the zombie driver, but the noise draws nearby undead, forcing a perilous escape with the vehicle.
En route to Incheon Port, they are ambushed by a rogue militia led by Sergeant Hwang Kim Min-jae. Their vehicles crash, killing one teammate and leaving another dead at Hwang’s hands. Chul-min hides in the truck while Jung-seok runs, only to be rescued by two sisters, Joon-yi Lee Re and Yu-jin Lee Ye-won. They bring him to their home, where their mother, Min-jung, and grandfather Elder Kim shelter him. Jung-seok realizes that the two sisters are the mother and daughter he had refused to help four years earlier.
The militia base holds Chul-min and forces him into brutal survival games that pit captives against shambling zombies. Private Kim discovers the money and spills the plan to Captain Seo Koo Kyo-hwan, who secretly intends to escape the peninsula with the truck. Meanwhile, Jung-seok tells Min-jung and her family that an extraction ship awaits at Incheon Port. Min-jung devises a bold plan to steal the truck and flee with Jung-seok and the others.
That night, Jung-seok and Min-jung infiltrate the militia base, holding Private Kim at gunpoint to extract information. They learn that Chul-min is still alive and halt the deadly game to rescue him. Chul-min narrowly saves Jung-seok from a zombie bite but is shot dead by Hwang. Min-jung fights off Seo and escapes in the truck with Jung-seok, yet their route is blocked by a growing herd of zombies. Joon-yi, Yu-jin, and Elder Kim arrive to distract the pursuing undead and provide a path toward their own vehicle.
Driven by pursuit, the two vehicles race through the night. Hwang and Unit 631 close in, but they are sidelined as the zombies catch up and eventually overrun their opponents. Hwang is killed by the very zombies he helped unleash, and Seo ambushes Incheon Port, taking Joon-yi hostage. Yu-jin’s quick thinking buys Joon-yi time to escape, though Elder Kim is fatally shot and Min-jung is wounded in the confrontation. Seo reaches the extraction ship aboard the truck, only to be betrayed and shot by the mobsters. As he dies, Seo reverses the truck to jam the cargo ramp, letting zombies flood the ship and slaughter everyone aboard.
With the threat continuing, Jung-seok and the family manage to signal a passing U.N. Chinook. Though Min-jung is badly hurt, she stays behind to hold back the oncoming horde so Jung-seok and her daughters can board the helicopter. Remembering Chul-min’s words about protecting his family, Jung-seok turns back to save her and fires on the advancing zombies. Min-jung escapes just in time, and the family safely boards the helicopter, finally evacuating the peninsula.
