The lure of languages and travel and a teacher's shove propelled John Emmerson, of snug Canon City, Colo., toward the foreign service; a chance to study Japanese that ""looked like a good deal"" landed him in prewar Japan; and through 30 years' consular duty he remained in spirit the impressionable subordinate. But the ""Japanese thread"" that Emmerson took up by chance was to lead through some curious historical byways and ultimately to his undoing. On U.S.-Japanese relations, 1936-41, he adds little to Ambassador Joseph Grew's record of frustration except swipes at the hawkish State Department officer who ""edited"" Grew's reports. About Japan, then and later, he is largely uncommunicative. But during a term in annexed Taiwan, Emmerson saw the Japanese policy of ""assimilation"" clamp down on the aboriginal headhunters (whom the Chinese had been willing to let be) and whip the Formosan populace into line (""This household speaks Japanese,"" read signs over designated doors). Come the war, Emmerson was sent to Peru to monitor the activities of the sizable, now suspect, Japanese colony; and, as the only non-Japanese to speak the language, fingered Japanese-Peruvians for deportation and detention in the U.S.--""a violation of human rights"" of which ""I am not proud."" His next, and crucial, assignment was to the China-Burma-India theater where--interrogating prisoners--he met ordinary Japanese and learned, as he tried (futilely) to tell his superiors, that they would lay down their arms in response to the Emperor's wish. Then it was over the Hump to China and Yenan, Mao's bastion, where Japanese Communist leader Nosaka ran a school for receptive prisoners--a group then ""opposing the same regime that we were determined to defeat."" The proviso is important because this involvement, plus Emmerson's attempt to foster an international Japanese antiwar organization and his postwar contacts with Japanese Communists--brought upon him (along with China hands John Davies, John Vincent, etc.) the charge of undermining Chiang and promoting the Communist cause. Though he was repeatedly cleared, his career was blighted (by, for one thing, 16 years ""exile from East Asia""); and, tragically, his testimony led to the suicide of Canadian diplomat Herbert Norman. It's an artless book but all the more convincing--especially on the revival-meeting euphoria of wartime Yenan, the unceasing internal-security persecution--for Emmerson's resemblance to an earnest, hapless Jimmy Stewart.