During World War II, even though the United States and the Soviet Union were allied against Germany, there wasn’t enough trust in the relationship to prevent mutual spying. Budiansky tells the story of U.S. efforts to crack the Soviets’ codes, which proved difficult to do after 1948, even with the benefit of the most powerful computers available. His story begins in the 1940s and ends in 1989, but a lack of declassified material from the more recent decades forces him to focus on the years prior to the mid-1960s. Budiansky ably guides readers through the technical details of code breaking and the bureaucratic wrangling that so often bedevils intelligence work. He illuminates a number of U.S. successes and credits the National Security Agency with helping demonstrate that the bark of Soviet leaders was worse than their likely bite. But he is also critical of the nsa’s missteps, including its tendency to capture far more material than it could ever hope to analyze and its readiness to spy on Americans at the behest of U.S. President Richard Nixon.