The FBI's file on the Soviet spy Otto Katz (1893-1952) called him "an extremely dangerous man." This label doesn't even begin to tell the story. Katz, a daring and treacherous Soviet spy, seemed perpetually to beat the center of crucial historical moments. A deft writer and litterateur, he talked Arthur Koestler out of a life-threatening but ultimately useless mission in the Spanish Civil War, and persuaded Hollywood's gentry to donate to the Hollywood...