When the TSA reacts to a terrorist threat in the form of a NYC subway train hijacking, they are interrupted by the NSA who are conducting their own investigation into the hijacker, a renowned virologist who stole his most dangerous creation from his lab.  But when they find that he is already mutating into an infectious monster and infecting and mutating the other passengers, the NSA and TSA must determine the best course of action to quarantine or destroy the train before a horde of infectious monsters gets unleashed on NYC.