When the Tree of Knowledge Falls : TO KNOW A WOMAN, <i> By Amos Oz translated from the Hebrew by Nicholas de Lange (Harcourt Brace Jovanovich: $19.95; 262 pp.)</i>

For everything there is a reason, and for 50-year-old Yoel Ravid, the protagonist of Amos Oz’s new novel, “To Know a Woman” (his 12th book to be translated into English from the Hebrew), the season is autumnal and one of mourning. Ravid, a dedicated operative of the Israeli secret service, returns home from an undercover assignment in Helsinki to discover that Ivria, his wife of many years, has died in a freak electrical accident. As a result, Yoel “dies” in large measure to himself.

Ivria, it seems, was everything to him, emotionally a near-identical twin and the mainstay of his otherwise restrained covert existence, his only love and, we learn “even when love had gone and given way in the course of the years, successively, or by turns, to mutual pity, friendship, pain” there were still “bursts of sensual flowering, bitterness, jealousy and rage, and again Indian summers flickering with sparks of sexual abandon, then vindictiveness and hatred and compassion again, a tissue of interwoven, alternating, ever-changing emotions, swallowed up in strange compounds and unexpected combinations, like cocktails mixed by a lunatic barman. . . .”

Yoel sees his past together with the late Ivria in biblical terms, as if from the Book of Genesis: “And the man knew his woman.” For Yoel, “the bond between them was knowledge.” So at the news of her death, his life seems to wither away. And so together with his own mother and his mother-in-law who have moved in with him and his adolescent daughter Netta, a mild epileptic whom he attempts to shelter from the tremors of the world outside their little suburb of Tel Aviv, Yoel withdraws into his widower-hood, resigning from the secret service and throwing himself into the daily round of household chores and gardening. He becomes a sleepwalker, moving through the diurnal/nocturnal cycle of house repairs, reading, gardening, and television and more television, retreating into a sort of anomic funk from which only an occasional fishing trip with his rental agent or, eventually, an on-again-off-again liaison with one of his next-door neighbors (an American woman who, along with her slightly perverse brother, has emigrated from Detroit) can rouse him.

Yoel’s grief seems to become so internalized that it can’t really be distinguished from the very air he breathes. Like the breeze that blows in from the sea “bringing a salty tang and a faint shade of melancholy,” his state of mourning both keeps him from acting and keeps him alive at the same time. But only his operative’s eye that allows him to see the world around him as a series of tantalizing interlocking ciphers that cry out for decoding keeps Yoel--and the novel itself--from lapsing into the complete somnolence of a burnt-out case. “During the twenty-three years he had been in the service,” Oz writes, Yoel “had perfected the art of . . . figuring out how he could crack the safe where the other kept his secrets.” Now, with Ivria dead, he still has his spy’s sensibility, but he seems to have lost his touch. And “at half past six in the morning in his own garden, a widower, unattached in almost every sense of the word, he felt the suspicion that nothing at all could be understood. That the obvious, simple, everyday things--the chill of dawn, the smell of burned thistles, a small bird among the apple leaves rusting from the touch of autumn, the feverish touch of the breeze on his bare shoulders, the scent of watered soil, and the taste of light . . . held a secret.”

But the retired operative seems clenched in the fist of his own grief, capable of seeing the questions posed by the world around him, but incapable of forming answers. “How can you know which is the right access code?” he asks himself. “How can you discover, among the infinite combinations, the correct prefix? . . . How could you be sure that it didn’t change every seven years, for example? Or every morning? Or every time somebody died?”

Life, meanwhile, changes around him, from the transformations in his mother’s health on through his daughter’s growth toward independence and his own oddly conducted but annealing affair with the woman next door. Duty, in various forms (from an urgent call from his old station chief to offers to go into a number of different enterprises from business to charity) cries out to him.

For a long season, Yoel puts these calls on hold, though now and then he finds himself attentive to the changes in nature. The breeze off the ocean blows cold, then warm. He tends to his garden, preparing it at last, after a long isolated period of chill, for spring. And though he usually has one eye on the television screen, watching the news and documentaries with Netta in their one mutual activity that doesn’t set in motion either his overprotectiveness or her adolescent disdain, Yoel’s got his other eye on the garden behind his apartment, and on the sky where in one privileged moment in early morning he catches sight of migrating storks flying “over the tiled roofs of neat houses, over gardens and woods and citrus groves, absorbed eventually among the feathery clouds brightening in the southeast. After the orchards and fields will come rocky slopes and stone villages, valleys and ravines, and then at last the silence of the deserts and the gloom of the eastern mountain ranges veiled in full mist, and beyond more desert, plains of shifting sands, and beyond them the last mountains. . . .”

Now and then in his past life, Yoel’s colleagues in the secret service would rave about a new spy novel they were all reading, “a new book by Le Carre, say . . . and once, years before, he had toyed with the idea of writing a little spy story himself . . . but he had dropped the idea because he could not find anything remarkable or exciting in his own doings . . . .” The reader of “To Know a Woman” will strongly disagree. We see little of Yoel’s work as a spy, but a lot of the ex-op in his painful first year of widower-hood. And the incremental changes Amoz Oz portrays in his character, for all of their everyday nature, add up to a transformation both remarkable and exciting.

By spying on the spy in his bereavement we come to know more than just a man and his hard-won knowledge of his woman, his life with her and without her. We come to know a little more about ourselves.