Just after 9/11, the U.S. was rocked by another deadly act of terrorism when letters containing anthrax were sent to unsuspecting victims. The anonymous assault claimed five lives and caused panic throughout the country. Despite inter-agency turf wars and several false leads, FBI investigators closed in on a shocking prime suspect: a scientist embedded in the top-security USAMRIID lab with unfettered access to the world's most deadly pathogens.