When a lightbulb falls in a subway tunnel, it releases a pathogen that could kill millions. While the mayor postures, people begin to die, especially on the city's grim West Side. Finally, the government acts, sealing off entire sections of the city but are they keeping people out or in? Meanwhile, Michael Kelly's hunt for the people who poisoned his city takes him into the tangled underworld of Chicago's West Side gangs and the even more frightening world of black biology.