The world waited anxiously for the other shoe to drop, according to this history of the fraught period between America's atomic bombing of Japan and the Soviet Union's 1949 test of its first nuclear device. Princeton historian of science Gordin ('Five Days in August') treats the era as a study in the pitfalls of incomplete information. American officials tried to keep nuclear technology secret (but not too secret: they fretted that not publishing crucial data would tell the Soviets what to look for) and conjectured endlessly about when Russia would get the bomb. Meanwhile, the Soviets, working from espionage and revealing American public sources, wondered whether their information on bomb making was trustworthy and struggled to overcome huge gaps in their knowledge. When American radiological monitors detected a Soviet nuclear blast in 1949, American officials worried about the geopolitical fallout from revealing their knowledge of the Russian success, which Stalin kept secret.