Two children die of a disease thought to be nonexistent in the United States. Within hours, thoroughbreds at the legendary Churchill Downs are dying of a virus that cannot be identified, even by the most expert veterinarians. Called in to solve these lethal mysteries, noted virologist Jack Bryne discovers the two bear uncanny similarities to the Fifth and Sixth Plagues described in the Book of Exodus. And the horror is just beginning...

Every month another monstrosity claims its victims. Every month brings the reenactment of another more catastrophic plague. Soon Bryne's own worldwide medical computer network, ProMED, is invaded by the power behind the horrors--a diabolically intelligent serial killer with a sophisticated knowledge of toxins and an obsession with a with biblical retribution. To make matters worse, the FBI is convinced Bryne himself is the killer.

Caught between both sides, the brilliant virus hunter joins forces with his bright lab assistant, an ambitious TV newswoman, and a young religious scholar to find this madman and stop him before it's too late. But even Bryne does not know how close the killer is...until he meets this modern medical Moriarty on a midnight confrontation that will determine the future of the world.