The diminutive monster (at only five feet tall) at the heart of the misery of Stalin's purges was Nikolai Yezhov, head of the NKVD (the forerunner of the KGB) from 1936 to 1938, the murderous inquisition's most intense phase -- not least because Yezhov pushed the process even harder than his master. This book, pairing an American historian and a Russian historian and published as part of the important Yale University Press series on Soviet history, seeks to explain who this man was, how he got to where he was, how he thought, and how free he was to act as he did. Their answers, in brief, are that he advanced by dint of his own effort and talent, largely by mastering, as Stalin had before him, organizational work and personnel management in a system that from a centralized bureaucratic nerve center decided where everyone who was anyone would labor. Well liked by his fellow workers as a young party activist, well thought of by his superiors as he made his way up the chain of command, and well skilled at doing in those who stood in his way, Yezhov, in the ultimate conclusion of the authors, was no cynic. Their truly chilling proposition is that "he believed what he said and believed in what he did."