WILLIAM BUCKLEY'S latest Cold War thriller takes Blackford Oakes to a trial in the Soviet Union, and the trial turns out to be his own. A decade into his career as a secret agent for the CIA, the ingenious and fair-haired Oakes has already saved England from a Soviet spy in the queen's court, protected Europe from a Soviet onslaught by killing a promising West German leader, and kidnapped a brilliant Soviet physicist who holds the key to the space race. These triumphs occurred in London, Paris, and in a village outside of Cologne, grand settings for choice incidents in an epic clash of ideology and power. Now the struggle moves to Washington, Moscow, and Berlin, where Oakes maneuvers to nab a Soviet mole in the CIA, and Buckley maneuvers to show us why, in the midst of efforts by Eisenhower and Khrushchev to come to some understanding, the U-2 affair was allowed to take place.

In Saving the Queen, the first and most refined of Buckley's biennial series, Oakes convinced Viscount Kirk, the queen's cousin and the uncovered court spy, to crash and kill himself during a duel of wits and jets piloted by the men at 600 miles per hour. Oakes proved his cool, and, also, his ability to fly, which, his followers know, he'd learned at seven, confirmed in a solo at 10, and made public as a young World War II fighter ace. He uses the skill again in Marco Polo, tracing an adventurous route along the Chinese-Soviet border 16 miles up (and "five thousand feet higher than the official record") in a black-bodied U-2 like the one actually flown by Francis Gary Powers when he was shot down more than 20 years ago. Oakes soars (and eventually falls) after again accomplishing what he's been prone to do on previous escapades: meeting a challenge of heart and mind; surveying the bounds of battle in the hidden war of politics and morality known as intelligence; and making peace with his girlfriend, Sally Partridge, the beautiful, aloof Chaucer scholar with whom "the ultimate consummation of marriage somehow did not materialize," then bedding another dazzling woman, who sides with the enemy.

Along with Oakes, the Marco Polo cast includes the Buckley regulars. Allen Dulles, who "did most of his thinking by soliloquy," directs the CIA. Rufus--Buckley's Smiley --runs Operation Tango, to root out the mole. As Buckley tells it, Churchill once snapped at the head of British intelligence: "If it hadn't been for Rufus, you would be reading Jane Austen in German." Anthony Trust and Singer Callaway, who keep Oakes primed for action, serve as key agency contacts. Dean Acheson--stiff, impatient, and knowing in his black derby and moustache -- plays a timely role as go-between within the American establishment and as an emissary to the Soviets. They make a witty, urbane, strong-willed crew, suited to suspense wrought by Buckley's selective memory and fancy about the Company and the men of its white-shoe heyday.

The Buckley regulars (and cameos like the "jut-jawed, beefy, all business" J. Edgar Hoover who reports to Rufus on the operation) give Marco Polo a nostalgic quality, the literary equivalent of filtered light. Here's ornery but sly Ike calling his Russian nemesis "Kroocheff," and the American hockey coach at the Squaw Valley Olympics crediting the Soviet team captain with suggesting that the U.S. team take oxygen to overcome fatigue and beat the Czechs, then the Russians, for the gold medal. In reminiscences about England's Greyburn College and Yale, Oakes jibes the institutions that represent the traditions he seeks to uphold. Like Buckley, Oakes winks merrily at a troubled world, but a stern conviction shadows his mirth.

Buckley uses the sense of distance created by nostalgia to clarify the symbols in each player. Sometimes he's outrageously specific, relying on the usual jawbreakers (brummagem, mephitic, nivellator, and repristinated, for example) to remind us that his vocabulary is broad and ours, narrow. Though he never rises to the level of a winning vignette in Stained Glass (Oakes goes to a late-afternoon show of The Caine Mutiny, sits next to Senator Joseph McCarthy, and slips him a note: "SENATOR: INVESTIGATE ALLEN DULLES!"), Buckley often dwells on brief encounters to make comments on kings, queens, even pawns. From the patrician slouch that marks his television posture and all his prose, Buckley's latest is a dashing historical chess game, whose moves God determines in favor of true believers. Brisk, droll, with pricks of the knight's sword landing on obvious targets, the game moves in mischievous patterns, even if we know black from white and how each will fare in the end.