Yoon Sae Bom is a special agent with quick wits and reflexes and another special quality. She earns the opportunity to move into a new apartment set aside for civil servants in a coveted apartment complex by pretending to marry high school friend Jung Yi Hyun. Yi Hyun is a detective investigating the spread of a mysterious disease. They are trapped in their apartment building when Han Tae Seok, head of the task force to control the spread of the disease, orders the complex to be sealed off from the rest of the city. Quarantine and disease reveal a social caste system, bringing out the best and worst of the apartment residents.