The film is set four years after the events of Train to Busan. The zombie outbreak that devastated South Korea has spread, leaving the country in ruins and under quarantine. The story follows a former soldier named Jung-seok (played by Kang Dong-won) who is living in Hong Kong. He is approached by a group of people who offer him a chance to return to the Korean Peninsula to retrieve a large sum of money left behind in the chaos.

Jung-seok and his team agree to the mission and return to the peninsula, only to find that the situation is far more dangerous than they anticipated. The area is now overrun by hordes of zombies, and they encounter a group of survivors who have established a makeshift community in the ruins. These survivors are not only fighting off the undead but also struggling against other human threats.

As Jung-seok and his team navigate the perilous environment, they face intense action sequences, emotional challenges, and moral dilemmas. The film combines high-octane action with moments of drama and horror, exploring themes of survival, humanity, and the impact of a global disaster on both the living and the dead.