Private Lee Jae-young serves in an air defense unit on the roof of a Gangnam high-rise. Although he and his partner are the oldest and clumsiest of the conscripts, it's not his military skills he's worried about, but his relationship with his girlfriend, Kang Young-ju. When Young-ju gets tired of his whining and suspicions, she suggests that they break up, but later decides to meet in person to talk. When the girl heads to Gangnam in the company of her estranged coworker, the people of Seoul are infected by a zombie infection.