Closed-off high school student Chha Hyun-soo rarely leaves his home and does not communicate with his family. One day, his entire family dies in a car accident, and he is left completely alone, having to move to a small apartment. At the same time, something strange begins to happen all over the world - people everywhere are turning into monsters. Hyun-soo will have to overcome himself and get to know his new neighbors better in order to confront the unexpected threat.