Eradicating smallpox in nature and confining official smallpox stocks to only two locations are impressive achievements: however, they are no guarantee that the world is now safe from a smallpox outbreak. The Demon in the Freezer calls attention to the fact that unofficial stores of smallpox may remain in the hands of countries other than the United States and Russia, and to the fact that a sample of smallpox could easily be engineered to create a supremely devastating bioweapon. Nor is smallpox the only stubborn menace of this sort. Preston’s account, after all, begins with a discussion of the 2001 anthrax attacks—an instance in which a deadly substance was spread through the U.S. postal system with little trouble. Perhaps the only factor that can keep such persistent biological threats in check is not regulation or research, but the more compassionate and responsible side of human nature.

At several points in his narration, Preston explains how the potentially life-saving work of smallpox and anthrax researchers can clash with the more day-to-day duties that these individuals face. Peter Jahrling must deal with the tasks of raising his daughters and of dealing with his wife’s worries, all while helping the U.