Dr Kay Scarpetta has begun to think the state of Virginia is the most recent stop on the travels of a psychopath, but before she can properly liaise with colleagues in different states and different countries, another body is found. Like the others it is discovered on a waste site, but Scarpetta sees evidence which makes her doubt it is the work of the same killer. As she follows the forensic footprints the victim's life draws her away from seeing the death as an individual killing, and leads her to face the probability that someone is on the point of releasing the smallpox virus back into a world which believes the disease has been eradicated - a belief which has led to all stocks of the vaccine being destroyed. Could such a mass murderer really exist, and what sort of mind would contemplate releasing such havoc?