Jang Byeong-tae is a small and weak boy living in Onyang in South Chungcheong Province. He's at the bottom of the school's social ladder and when he transfers to the neighboring Buyeo Agricultural High School, he faces an unexpected incident that becomes a turning point in his life.

Jae-yoon, a late military enlistee, and his girlfriend, Young-joo, break up over the phone over growing misunderstandings. But a zombie outbreak rocks the world. A national emergency is declared, a plane crashes in the city center, and Jae-yoon and his unit get trapped on top of a Seoul skyscraper. Young-joo risks the zombie-filled streets to find him. Can their love survive the apocalypse?

On a Christmas Eve, a lifeless body of teenage boy is found. The victim's revenge-driven twin brother checks himself into a juvie to hunt down the suspects.