When a mutated HIV virus causes a global epidemic, one city in the American Southwest builds a wall that divides the city into two zones, separating the infected from the uninfected. As the epidemic continues to spread, unrest grows in the South Zone, where the infected are quarantined. Now in the scorching heat of summer, their power has gone off, and it can only be a matter of time until the wall fails to hold back the coming firestorm of violence. When that happens, will any place be safe? 25-year-old Sarah, who has sought refuge in the city after losing her family, lives in the North Zone and teaches children orphaned by the epidemic. To shield herself from more hurt, she distances herself emotionally from others, but she can't turn her back on everyone. Someone has to help the elderly woman who lives down the hall. And then there is the orphan Indian girl in her class who will be sent to a reservation to die unless she can prevent it. And how can she say no to Martin, the young hospital orderly from the South Zone who shows up at her high-rise with a bullet wound and a dangerous request? As the crisis escalates, Sarah must overcome her past trauma and join forces with friends and strangers to save the people she cares about. She must decide who she can trust and what risks she is willing to take, including the risk of letting herself love again.