A vivid generation-spanning dossier on the Walker clan that dramatically details how, for nearly two decades, its paterfamilias made spying for the Russians a family affair. Blum (Wanted!) traces the career of amoral, manipulative John A. Walker Jr. from his scapegrace youth in Scranton, Pa., through a 21-year tour in the US Navy and guilty plea to espionage charges in 1985. Ironically, Walker (who turns 50 in October) found a home in the Navy, becoming a communications expert and rising to the rank of warrant officer. Sailor's pay, however, was not enough for a gamesman with an alcoholic wife, kids., and an expensive, two-timing life style. In 1968, he walked into the Russian embassy with secrets to sell. Before he was finally caught, the sometime submariner had betrayed a wealth of cryptographic and other highly classified material to the receptive KGB. Walker also recruited his brother, son, and best friend as Soviet agents. The poorly recompensed group did incalculable harm to America's security, giving the USSR the means to decipher over one million military messages, plus vital information on weaponry, tactics, ship movements, and related matters. Blum's switched-on saga makes clear that Walker relished life on the edge. Though a generally disciplined subversive, he was sloppy in his personal affairs. Eventually, Walker's embittered ex-wife (who did not realize he had involved their son) turned him in. With a surfeit of dubious tips in its files, the FBI did not act for four months. When the Bureau and other intelligence services got into gear, though, they blew a chance to nail Walker's KGB control. Blum does not dwell on lapses of this sort or the lax procedures that gave lower-echelon sailors like Walker comparatively easy access to ultrasecret data. Instead, he focuses on the spy ring's globe-trotting mastermind, his confederates, and members of their families--apparently ordinary people playing at a dangerous game whose stakes are beyond reckoning. Blum--who has an eye for detail and a knack for narrative--keeps the pot boiling briskly throughout. Unfortunately, his meticulously documented thriller is fact, not fiction--as disturbing as yesterday's, and perhaps tomorrow's, headlines.