A drama about a mysterious disease that spreads at an alarming rate and the doctor who is tasked to solve what is causing the mysterious illness before thousands of people die. Kang Joo Hun is director in charge of the disease's epidemiology or epidemiological investigator. He is a former officer from the military police who has natural born insight and is at risk of losing his loved one to the virus. Lee Na Hyun is his lover who is taken by the virus when it's out.