An urban quarantine happens in Atlanta following a deadly outbreak of a mysterious disease.

Lex finds out that a woman who had close contact with an infected patient has disappeared.

Dr. Cannerts makes a major breakthrough that brings him one step closer to finding a cure for the virus. Meanwhile, after monitoring hospital surveillance from the day of the outbreak, Katie and Jake unravel the truth behind Patient Zero. Elsewhere, Jana and Suzy move forward with a plan to escape the cordon using the city’s underground tunnel system. Finally, a risky operation to extract the potential antidote from the cordon takes an unexpected turn.