When a mysterious and deadly epidemic breaks out in Atlanta, a vast urban quarantine is quickly enforced. Trying to keep the peace on the streets is police officer Lex Carnahan, who has quickly risen through the ranks of the Atlanta PD. But Lex's job becomes even harder when he learns that his longtime girlfriend, Jana, and his best friend and fellow officer Jake, are trapped within the cordoned area. Also quarantined within viral ground zero is 17-year-old Teresa, who is eight months pregnant and now separated from her boyfriend on the other side; Katie Frank, an elementary school teacher now placed on lockdown with her entire class, including her young son; and CDC researcher Dr. Victor Cannerts, the doctor who initially made the controversial call to quarantine the area, and who is now racing to find a cure for the virus. On the outside, Dr. Sabine Lommers leads the government efforts to contain the outbreak, and asks for Lex's help in enforcing the cordon – which grows increasingly difficult as the public trust deteriorates.