The government has begun taking steps to cope with the possibility of a terrorist attack involving smallpox by training doctors to recognize the disease and by vaccinating small teams of experts who would rush to any part of the country to contain and treat a suspected outbreak.

Russia's decision to blow an aerosolized form of a powerful narcotic through the ventilation system of a theater to end a hostage crisis raised anew an inevitable and terrifying question: what if a terrorist unleashed a potentially lethal chemical in this country?

The author interviews epidemiologists and bioterrorism experts to assess the risks of a new pandemic.