More than a high-stakes espionage thriller, "Fallout "painstakingly examines the huge costs of the CIA's errors and the lost opportunities to halt the spread of nuclear weapons technology long before it was made available to some of the most dangerous and reckless adversaries of the United States and its allies.

For more than a quarter of a century, while the Central Intelligence Agency turned a dismissive eye, a globe-straddling network run by Pakistani scientist A. Q. Khan sold the equipment and expertise to make nuclear weapons to a rogues' gallery of nations. Among its known customers...