After the disaster at the Chernobyl nuclear plant in 1986, Soviet officials asked Medvedev, the chief engineer in Chernobyl at the time of its construction in 1970, to return to the reactor to determine the cause of the accident. Medvedev's eloquent and troubling, though sometimes confusingly technical, account of the catastrophe is the result of that inquiry. By reviewing the history of nuclear disasters in both the US and the Soviet Union, Medvedev initially makes the point that nuclear error is more common that is generally thought. Then, relying heavily on testimony and interviews, he focuses on the concatenation of mistakes that resulted in the explosion of gas within Chernobyl's nuclear reactor. Medvedev presents the story as a countdown, stopping at each point to inquire whether the disaster could still have been averted. His analysis of the breakdown of the reactor, and the simultaneous failure of the reactor's coolant systems, may be difficult to follow for the nonengineer. However, his horrifying account of the medical effects of the disaster on the operators, on the firefighters who heroically and suicidally worked to put out the nuclear flames, and on the entire surrounding town and area dramatically illustrates the terrible consequences of nuclear accidents. Also, his sardonic portrayal of the reaction of public officials to the disaster demonstrates the dangers of ignorance in high places. Although lay readers may not easily follow the sophisticated analysis of the causes of the accident itself, Medvedev's powerful and highly dramatic presentation of the dangers of nuclear energy comes through loud and clear.