The worst epidemic ever seen sweeps through Bundang, a suburb of Seoul. After smuggling illegal immigrants into the country, Byung-woo dies from an unknown virus. Soon after, the same symptoms plague scores of residents in Bundang. People are helpless against the airborne disease and the number infected increases quickly, spreading chaos. As a worst-case scenario precaution, the government orders a complete shutdown of Bundang, the city of a half million people just 19 kilometers from Seoul. Meanwhile, infectious disease specialist In-hye and rescue worker Ji-goo go into the closed city to find a blood serum that will be the key to developing a vaccine.