By Margot Mifflin
Updated May 01, 1992 at 04:00 AM EDT

Her method was seduction, her victims were diplomats, and her work affected the outcome of World War II — or did it? Mary Lovell (Straight on Till Morning) has written, Cast No Shadow: The Life of the American Spy Who Changed the Course of World War II, a lively biography of Betty Pack, a Washington, D.C., aristocrat turned Allied spy who inevitably fell in love with the men whose hearts and secrets she stole. But despite its conclusive subtitle, Cast No Shadow casts a big shadow on Pack’s importance by revealing, in the end, that a previous biographer’s claim that she changed the course of the war was ”not generally taken too seriously.”

Still, there’s no doubt that this wily Mata Hari handled hot assignments, traveling to Warsaw, Chile, war-torn Madrid, and occupied Paris, then home to Washington, where she stole the Vichy French ciphers that may or may not have facilitated the successful Allied attack on North Africa in 1942. Because Pack, who died in 1963, was an opaque (and not entirely sympathetic) woman, Lovell is never quite able to get inside her mind, but she does describe her adventures colorfully, and offers a fascinating snapshot of military espionage in its infancy. B+