Diplomat-traitor Donald Maclean was, according to Noel Annan's splendid foreword here, ""the only one of the six main spies who found the actual practice of deception and concealment distasteful."" The book that follows, more sturdy than splendid, fills out that thumbnail sketch--with social background, fresh details (from recent research), a soupcon of psychology, and plenty of insider-knowledge about Britain's Foreign Office. (Cecil worked with, and for, Maclean in the Thirties and Forties.) Son of Sir Donald, a famous middle-class politician and stern Presbyterian, young Donald grew up as half rebel, half stoic: an outward and quasi-genuine conformist, ever dutiful; but also a repressed homosexual, an incipient alcoholic, and a fiercely dedicated Marxist--with an ideological commitment that began at prep school and thrived at Cambridge. Soon recruited to work for the Comintern (not, at first, for the USSR per se), Maclean pretended to lose interest in Communism and began an industrious career in the Foreign Office, stationed in Paris before WW II. In the late 40's, he moved on to a key position at Britain's embassy in Washington, D.C., leaking vital data to Moscow; above all, he kept the USSR current on US nuclear capabilities, thus fueling the atomic-weaponry race. (On the other hand, during the Berlin Wall crisis, Maclean's reports ""may have contributed to preventing a cataclysm."") But the pressures of his double life led to near-breakdown, self-destructive sprees, rising suspicions--and defection in 1951: he spent the next 30 years in Russia, teaching and writing, estranged from wife and children, unrepentant yet far more somber than Burgess or Philby. Cecil, a very Establishment sort, works hard to explain how the Foreign Office's high-minded, good-hearted values made Maclean's deceptions possible; he scoffs at FBI exaggerations of Maclean's villainy and British stupidity. These arguments--like Cecil's sketchy psychological close-ups of Maclean and wife Melinda (never a co-conspirator, Cecil believes)--are only half-convincing. But, delivered in a crisp, literate, no-nonsense style, this compact biography offers an agreeably narrow focus on a spy-tangle that often seems dauntingly dense.