I finished the book, as much as I tried to take it nice and slow. It isn't really the kind of book you can take nice and slow. There are three sections throughout the book, called Invisible History I, II, and III. Preston pauses the action of the story to talk about events in the history of biological warfare and the development of biological weapons. Normally history lessons like this are pretty boring and I just want to get back to the story, but they actually were interesting and I learned SO much about bio weapons. Preston makes everything in his stories so realistic and accurate through all the research he does, so it kind of felt like half the time I was reading about something that was real. 

Through some witty forensics and a lot of digging, they track down the man who has been setting the virus (the Cobra virus) on the city. They connect the virus to Lesch-Nyhan disease, which is a terrible, rare genetic disease in boys that causes violence, self-cannibalism, and other nervous system problems. The last few scenes are really intense and suspenseful because the terrorist guy suspects that they've found him, and they don't want to rush in and grab him because he might set off a bunch of virus bombs. At the end he's beginning to show the effects of having contracted Cobra himself, which is scary because people go berserk and violent when they get it. Then there's a crazy chase between him and the two main characters all through the subway tunnels of Manhattan. It ends up being a lot like the climax of Silence of the Lambs.