Nathan Turner, a member of the Army Reserve, is called up one night. Part of his unit gets sent to Washington, DC, to aid forces in trying to contain a strange virus that is quickly infecting people. As the infected attack a safe zone camp he is assigned to, Nathan ends up saving Chelsey, an eight-year-old girl. After the military bombs DC, he and Chelsey make their way to the harbor to leave.
They find a downed helicopter with a mysterious woman named Melissa, who is badly hurt and unconscious. He spends a while nursing Melissa back to health and saves her life. They both fall in love while trying to find her dad, who can help get them to safety and an understanding of what is going on.