"pilgrim" is an american former intelligence agent known as the "rider of the blue" who later writes a book on forensic pathology. pilgrim becomes involved in a case in new york city where a mysterious woman uses his book to commit untraceable murders in the aftermath of 9/11. the "saracen" is a saudi who becomes radicalised by watching his father's beheading. he later trains as a doctor and fights in the soviet–afghan war. pilgrim is recalled to the intelligence community who have detected a threat involving the saracen, who has created a vaccine-resistant strain of the variola major virus.