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-Wook), fight against these monsters and try to survive.