It recounts his WWII experience analyzing bombing data at the RAF Bomber Command. Aside from providing a compelling historical insight, which it most certainly does, in it, he recounts Smeed's Law (Reuben Smeed was his boss), which describes death rates due to traffic accidents in a manner divorced from national differences in safety regulation, road conditions, car design, or any of the other things one would imagine might make a difference in a matter like this.
The equation: the number of deaths equals .0003 times the 2/3 power of the number of people times the 1/3 power of the number of cars. He says it mostly holds true, to within a factor of two, for all countries and all time. After doing the calculation, using 300 million US citizens, 238 million registered vehicles, and some rusty math skills, Smeed's law does, indeed, hold to within a factor of two of American road fatalities. The Smeed equation gives 83,316 deaths and the real number is 43,443 for 2005.
Dyson posits that Smeed's law is saying that the national death rate from traffic accidents is dependent on the psychological constant that any population applies to accident death: above it, they drive more carefully; below it, they drive more recklessly...until they bump up against that psychological barrier and correct again by driving more carefully.