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Reciprocal racial hatred between Orientals and Occidentals was a theme throughout the intelligence reports, but the abuse didn't always follow ethnic lines. Japanese businessmen who were found to be excessively profiteering assets that could have gone to the Japanese military suffered some of the harshest beatings. Some guards expressed a hatred for white colonialists but seemed simply to be sadists, prompting the American Opfer to observe of the Japanese: ''They are inherently, I think, a cruel people.''

Another American repatriated from Shanghai was Lionel Stagg, described as a ''soldier of fortune'' who ''bummed'' his way to Shanghai on a tramp steamer and found work driving a Red Cross ambulance on a route covering 30,000 miles.

He seemed unconvinced by accounts of Japanese abuse. ''Certainly there have been some scattered atrocities, but they have been widely exaggerated and disproportionately published in the American papers,'' he said.

Yet it's also clear that the Japanese captors became increasingly more violent when passive resistance among the locals impeded their ability to manage the war. The secret files contain accounts of Japanese inquisitors in China threatening to harm the wives and children of interned Allied men suspected of hiding their wealth.

''To obtain information from the Chinese and the white people, the Japanese resort to severe third-degree methods such as beating them up and using every conceivable torture such as the water method, sticking splinters under their fingernails and beating them until they were unconscious,'' wrote Fred Sasel, an American who worked as a customs agent in Shanghai.

The desperate need for workers to mine, forge, build, and maintain the large but fragile empire seemed to play more of a part in the use of slave labor than cavalier cruelty. In Shanghai, the Japanese resorted to staging fistfights on busy streets, luring large crowds that were then dragooned into labor gangs.

Sometimes, people escaped. One intelligence report from July 1943 is attributed only to a ''reliable American'' who clearly was a diplomat or spy of some stature. His escape from custody in Japanese-held Beijing is a sampling of the surreal complexities of what was truly a global conflict encompassing myriad animosities.

China was a battleground for invading Japanese, Chinese communists, nationalist warlords, and Allied forces. This unnamed American, deducing that war was imminent just prior to the attack on Pearl Harbor, made contact with communist guerrillas who controlled the countryside, and persuaded them to help Americans flee if war broke out.

The day after Pearl Harbor, the American was confined to his quarters at the US consulate. Two weeks later, a Chinese-American college student who had returned to fight alongside Mao Zedong's revolutionary forces managed to elude Japanese guards and spirit the American out of the city. Before fleeing, however, the American urged other Americans and British to come along, but all refused.