Cha Hyun-Su (Song Kang) is a high school student. He is also a recluse and rarely leaves his room. He refuses to talk to his father, mother and younger sister. One day, his whole family, except for him, dies in a car accident. Cha Hyun-Su is left all alone. He moves into a small apartment. At this time, a mysterious phenomenon of humans turning into monster occur all around the world. The residents of Cha Hyun-Su's apartment building, including Pyeon Sang-Wook (Lee Jin-Uk), fight against these monsters and try to survive. Residents of Green Home Apartments, including Cha Hyun Soo, fight against monsters to leave their base and venture out into the world. At a baseball stadium, survivors from all over begin to live together. They are threatened by the monsters outside and also by the monstrous desires of the people among them.