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.

While Lex attempts to maintain control outside the cordon, he learns that a young woman, who had close contact with an infected patient, is unaccounted for. With limited resources available, Lex is forced to enlist help from Jake, whose growing resentment towards Lex for getting him trapped inside is causing him to spiral. Elsewhere, Katie attempts to keep it together as she keeps a watchful eye over her students, while Teresa is devastated to learn that her friends may have been exposed to the virus. Finally, Jana, who has learned that her best friend Suzy is also trapped inside the cordon, rations out their limited food as they wait out the 48-hour quarantine.

Following the release of several controversial videos depicting the chaos going on inside the cordon, Lex pleads with Dr. Lommers for additional reinforcements to be sent in. However, when the request is denied, Lex is forced to rely on a reluctant Jake to take control of the situation inside. Elsewhere, Katie has a tense stand-off with one of her student's desperate parents, while a robbery at her mom's store leaves Teresa shaken to her core. Finally, when Leo releases more damaging videos, drastic measures are taken to shut him down.

As the situation inside the cordon grows more dire, Lex's frustration builds as he becomes increasingly conflicted by the messages of false hope he's being forced to send to the public. When Jana suspects something is off with Lex's demeanor, she realizes the situation may be more serious than the government is letting on and devises a plan to reach Lex directly. At the hospital, Dr. Cannerts continues working towards finding an antidote, while Jake helps Katie cope with some personal issues. Elsewhere, Leo becomes concerned for his friends inside the cordon and turns to an unlikely ally to help him. Finally, a turn of events at the grocery mart leaves Teresa and her mother in a terrifying position.

Tensions between Lex and Dr. Lommers reach a boiling point after they disagree over how to execute a much-needed food drop inside the cordon. With limited resources on his side, Jake's attempt to control a desperate and hungry crowd leaves him rattled after a group of thugs show up and a stand-off ensues. Meanwhile, when the timeline of events leading up to the outbreak doesn't add up, Katie sets out in search of the truth.

As life outside the Cordon returns to normal, Lex moves forward with an attempt to reveal the truth about a possible government cover-up; Katie and Jake search for a missing person; Xander and Teresa plan their escape.

Lex clashes with Capt. Scott; the data recovery center comes under attack; a desperate plea from Jana leaves Lex's world in chaos.

A major breakthrough brings Dr. Cannerts closer to finding a cure for the virus; Katie and Jake discover the truth behind Patient Zero; Jana and Suzy plan to escape the cordon through an underground tunnel system.

As tensions reach a fever pitch inside the cordon, mobs of angry protestors take to the streets in an attempt to break free. Meanwhile, stuck in isolation and cut off from their chain of command, Lex and Dr. Lommers have no choice but to stand by helplessly as the cordon erupts into mass chaos. At the hospital, Jake attempts to lighten the mood by taking Katie on a date, but their happiness is short-lived after they discover that several of Katie's students have gone missing. Meanwhile, with Lex nowhere to be found, Leo moves forward with their investigation, inching one step closer to uncovering the person responsible for the outbreak.

When Teresa goes into labor, Jana, Suzy and Sam band together to turn Bitscan into a makeshift delivery room. Meanwhile, after spending some time with Dr. Lommers, Lex grows concerned after noticing a sudden shift in her behavior. Elsewhere, Leo continues to unravel the conspiracy behind the virus outbreak, while Jake stumbles upon some damning information about who may be involved. Finally, fed up with his lies, Katie confronts Dr. Cannerts.

Lex and Leo clash over their next move after a failed plan threatens to unravel their entire case. When word begins to spread that there may be a way out of the cordon, Jana considers her options. Finally, an unexpected turn of events brings Jake and Katie closer than ever.

As Jana, Sam and Suzy pull together the funds they need to plot their escape, Jake considers his own options for breaking out of the cordon. Lex receives cryptic clues from Leo that lead him to an abandoned warehouse outside the city. Elsewhere, a widespread rumor leaves Dr. Cannerts' life in danger. Finally, after seeking shelter at her grandma's house, Teresa makes a difficult decision about her family's future.

With only one shot to take Dr. Lommers down for good, Lex carefully plans his next steps. Jana Suzy, Teresa and Xander make their dangerous escape out of the cordon, but unexpected road blocks threaten to destroy their chance of making it home. Inside the cordon, Dr. Cannerts and Jake make a breakthrough discovery following a risky experimental treatment. Finally, with time running out, Lex is forced to make a decision that will change his life forever.