There's no knowing about Sidney Reilly, even now--no reconciling the PBS series, Reilly: Ace of Spies (to be shown again in 1985), with the anti-Bolshevik adventurer in Nigel West's new MI6 (p. 1004)of the anti-Bolshevik hero on display here. Reilly, we do know, was born Sigmund Rosenberg, a Russian subject, in 1874; the name Reilly he got (variously, according to the source) from the British widow he married in 1898 (his first or second wife, depending). On when he left Russia, and why, or what he did before joining the British Secret Intelligence Service (at an indeterminate date), Kettle tends to let his untrustworthy subject be his guide. Reilly enters history, in any case, as a British agent involved first in the ill-fated 1918 Cromie scheme to destroy the Russian Baltic fleet (lest it fall into German hands). About his murky conspiracy to murder Lenin, Kettle writes at considerable, inconclusive length--questioning whether, indeed, assassination was his aim. Even more of a tangle, and more disastrous for the Allies, was whatever Reilly did in 1919 to aid White Russian forces in South Russia. Back in the West, he unsuccessfully sought British financial assistance for the Whites (with some support from arch anti-Bolshevik Churchill). ""If the Allies, and particularly the British, has been prepared to carry out his recommendations, then things might have gone very differently."" Still anticipating a Bolshevik collapse, Reilly next put his weight behind terrorist Boris Savinkov--who, however, fell prey to a truly cunning (if true) Bolshevik counterespionage plot which eventually sucked in Reilly himself, or seemed to (he returned to Russia, and died there, in 1925). . . but not until after his forged ""Zinoviev letter"" had, as he hoped (or didn't), brought down the British Labour Government and discredited its trade treaty with the Soviets. The latter part of the story is tantalizingly detailed, at least--but for the first two-thirds or more, Reilly is a speculative construct in a morass of anti-Bolshevik intrigue.