From Boyd, a breathtaking, brilliantly twisted thriller

Restless
By William Boyd
Bloomsbury, 324 pp, $24.95

William Boyd may not quite rank as the finest living English novelist -- the choice could be disputed among Barry Unsworth, Ian Mc Ewan, David Mitchell , and the oddly devastating Jim Crace -- though he is not far off. He is master, though, of the most various kinds of fiction. (Mitchell, still young, comes close.)

There is the comically satiric portrait of a young neocolonial Brit in the early ``A Good Man in Africa"; the American road menagerie of ``Stars and Bars"; the Garc ía M árquez-like sweep of romance and wild ingenuities in ``The Blue Afternoon," set in the Philippines in the early 1900 s; and an extravagant rendering of 80 years of British decline by the wonderfully unreliable and touching coxcomb who narrates ``Any Human Heart."

These are only some conspicuous examples. All of Boyd's novels are instigated by a half-hidden social or historical sensibility, a subtle intelligence , and, should this seem dry, an infectious pleasure in the world's ways and how they work on one another. Such qualities nourish the evocation of a complacent Western civilization rendered absurd in its encounters with other cultures.

The absurdities are the joy of Boyd's books, along with a juggling mastery of story and character, and a style that is both lean and generous. There is a downside as well, best thought of as too-muchness: a character or sub-story too many or developed too far, and draining a little speed and precision from the juggle.

``Restless" is one more example of Boydean variousness, as well as large talent and, if you like, small flaw. As if he'd challenged himself to match a John le Carr é or Alan Furst, he has written an international thriller. It tells the breath taking and breath takingly gnarled story of Sally Gilmartin, a respectably settled old Englishwoman -- country cottage, comfortable means, assiduously tended garden -- who was a wartime spy.

She was also the victim of a deadly betrayal. It has made her live in perpetual fear. Even after arranging a terminal revenge near the end of the book, she remains finally undelivered. Once a spy's fear and suspicion become a life, life they remain. Thus the historical sensibility that runs beneath Boyd's happily skilled play of ``N ow you see it, now you don't, and now what you don't see is stood upon its head."

He tells the story partly through Sally's daughter, Ruth, an unquiet young woman. Ruth has her own difficult story, but it tends to distract (Boyd's too-muchness, perhaps) from the mission that starts when she finds her mother agitatedly scanning the nearby woods with binoculars.

As she leaves, the old woman hands her a folder inscribed ``The Story of Eva Delectorskaya." It is her real name. ``Gilmartin" -- he was the late husband she married years before -- is the last of a chain of identities she'd used to hide from her betrayer and pursuer.

The folder is one of a series doled out to Ruth as she carries out the task that Eva gives her: to learn the present identity of her enemy, locate him , and interview him. How she does it is a tautly expansive job of detection.

It is all in preparation for the confrontation that Eva herself will stage in a climax and a splendid anticlimax. Boyd's special virtue is that whatever high-flying action he arranges for his protagonists -- in this case, the breathless action of a thriller -- he doesn't scant their obstinate humanity. To act never takes fictional precedence over to be.

As Eva's past is revealed, folder by folder, its deeper drama is the beating heart beneath the dramatics of the present. We see the young Eva, a Russian refugee, living with her father in Paris just before the outbreak of the war. They are in mourning for Kolia, her brother, murdered as he attempted to infiltrate a pro-Nazi group on behalf of British intelligence.

Soon a stranger approaches her and introduces himself as Lucas Romer. A man of charm and assured presence, he displays a complete knowledge of Kolia and her family, and persuades her, initially reluctant, to join the same clandestine service.

She goes to Britain, undergoes rigorous training , and, under the leadership of Romer, who will become her lover, undertakes a series of missions in Belgium and Holland on the eve of the German attack. Boyd relates all this with a brilliant balance of mystery and revelation .

Romer takes Eva to New York, where he is assigned to set up an elaborate information and disinformation service aimed at arousing anti-Nazi feeling among an American populace still largely unwilling to come into the war. (Boyd uses historical materials, some only revealed years later, to describe the group's work .) Eva is sent on a mission to the Southwest to plant evidence purporting to show German plans to control South America.

She is betrayed, almost killed, discovers the identity of the agent inside her headquarters, realizes she is a target , and begins a long and involved series of flights and switched identities that ends in illusory safety in her cottage. (Several of her former colleagues, presumably on the trail of the double agent, have met mysterious deaths.)

Some of the brilliantly twisted plotting of that flight, with Eva seeking to outguess and outbluff her antagonist, becomes almost too difficult to follow. But difficulty in a thriller, as in poetry, may not be a flaw.

Richard Eder reviews books for several publications.