Tristão and Isabel, the hero and heroine of John Updike's 16th novel, Brazil, never quite realize the epic valor of their name-sakes of medieval legend and Wagnerian drama. They mean well, but they just can't seem to resist silk shirts and kinky sex.

The knight-errant, Tristão is strutting the Copacabana beach in his shining armor of night-black skin when he first lays eyes on pale Isabel, in her bikini and rich-girl languor. “This dolly,” he declares, “I think she was made for me.” With a razor blade in his pocket and the vague sense that he has outgrown a life of crime, Tristão makes his way to her, pledging his devotion with a D.A.R. ring previously snatched from an elderly North American tourist. Thus begins a new life of crime, for their love will force Tristão and Isabel to break all the rules of class, race and social convention. Even so, Tristão has a hard time giving up prostitutes and his razor blade. Isabel develops a habit of stealing family heirlooms to finance her marriage, and she shrugs off a lifetime of infidelity by reasoning that her spirit has remained true.

In an afterword, Mr. Updike cites Joseph Bédier's “Romance of Tristan and Iseult,” which he says gave him his tone. But these new lovers seem to have more in common with Othello and Desdemona, Romeo and Juliet, and perhaps Sean Penn and Madonna. They are not merely doomed but also adolescent and wildly foolish. To say that they loved “not wisely but too well” is in this case a kind of comic understatement.

The author has left his favored fictional terrain, the metaphorical deserts and jungles of suburban American marriage, for the very real deserts and jungles of class-engraved Brazil. The novel recalls an earlier work, The Coup, which was set in the mythical African nation of Kush. Because Brazil lacks the gentle, trenchant realism that is Mr. Updike's trademark and glory, it may at first seem slight to his seasoned fans. Some readers will also, undoubtedly, grow tired of the onslaught of rape fantasy and racist imagery. The novel is thoroughly salted with phrases to make the politically sensitive reader cringe: in their fantastic journey across the Brazilian hinterlands, the lovers encounter innumerable varieties of so-called Indians who scowl and steal children or flee “with the unembarrassed cowardice of savages.” There are ubiquitous references to Tristão's “yam,” the organ that arises (so to speak) as the book's central character, and whose monstrous size is explicitly linked with Tristão's African ancestry.

But a writer of Mr. Updike's accomplishment cannot be dismissed without a hearing. Brazil, for all its political incorrectness, seems good-natured and bent on self-parody, in exactly the same way his Harry (Rabbit) Angstrom—especially in the last of the series, Rabbit at Rest—winds up personifying flawed maleness.

My own many volumes of Mr. Updike's work have their margins blotted with scrawled protests—mainly the question, “Does he expect to get away with this?” He does, and he will. Whatever one feels about Mr. Updike's world view, it is hard to resist the depth of his mind and the seduction of his prose. Once again, in Brazil, that prose is measured, layered, insightful, smooth, as addictive a verbal drug as exists on the modern market. For every tiresome appearance of Tristão's yam, there is also an image or observation that seems, against all odds, to mark the arrival of something new in the English language.

Mr. Updike's characterizations are quick and deadly. All the many people who move outside the sanctified love zone of Tristão and Isabel are minor but unforgettable. César, the hired hit man, lectures Isabel on morality and Brazilian history as he kidnaps her (“The Portuguese did not bring to the New World the discipline and austerity that the Spanish did,” he explains. “If we were not as cruel as they were … it was because we were too lazy to have an ideology”), and he outlines his plan to retire and become an eco-tour guide: “Only Siberia and the Sahara can rival Brazilian vastness,” he points out, “and they have deplorable climates.” Isabel's widowed father is also a standout, as the impeccable, slavish diplomat whose “flavorless” Portuguese and melting profile play counterpoint to his daughter's Brazilian willfulness. “He knew so many other languages,” she observes during one of his paternal lectures, “that his mind was always translating; his tongue had no home.” The practical old man explains to her that love is a dream, “as all but the dreamers can see,” then adds, “It is the anesthetic nature employs to extract babies from us.” We recognize the voice as authorial, even as we refuse to believe what it says.

Tristão's mother is perhaps overdone, even for tragicomedy, as the torpid, whoring slattern. But his brother and sister-in-law are splendidly drawn as they claw their way to the middle in the industrial suburbs of São Paulo. “Chiquinho and Polidora seemed to him a couple crouching as they moved down a narrow corridor, with flaking paint and leaking walls, bumping their heads every time they tried to straighten up, never coming to the large room they envisioned. … Instead, they had this long apprehensive creep together under flickering light bulbs, while their bones turned brittle, their skin shriveled, and their hair fell out.”

True love promises the way out of every prison: deprivation or materialism, crime or innocence, blackness or whiteness, ignorance or pedagogy. As Isabel and Tristão flee their disapproving families and run westward from Brazil's colonized shore, they also move backward through time, through Brazil's colonial history, past mestizos and Indians and even a lost band of Portuguese conquerors, until the imposed covenants of class are irrelevant and no longer keep them separate.

If they could have stopped there, Tristão and Isabel would have slipped through the cracks of tragedy. But they are better than this. In their sunbaked life of hardship, they gradually merge. Then, in an act of primordial magic, they move through and beyond the gulf that once divided them. When they come out standing on opposite shores, Isabel and Tristão have changed places. “Black,” the book's opening line promises, “is a shade of brown. So is white, if you look.” Passionate love is the embodiment of empathy. The promise is fulfilled.

If the book's surface is sometimes a little sticky, its allegorical underpinnings are graceful and firm—and maddeningly circular. In the folds of a mythic, slightly funky love story, the magician John Updike has concealed layers of contradictory acknowledgment of the workings of the world. In the very last moment, he transcends wisecracks and holds fast to drama. Brazil is the tribute of a man in his 60's—a little cynical by reputation—to the youthful religion of love.

By the time everyone has had a chance to sing, this “Tristan and Isolde” is an operatic lament for the things we leave behind, as nations and as animal selves. The story pivots on the moment when Isabel must give up the D.A.R. ring, in a bizarre sacrifice through which she both saves and loses Tristão and herself. “Heartsick, she slipped off the inscribed ring and set it in the shaman's cupped hand. … As if a tooth had been knocked from her face, she knew she would never get back what she had just surrendered. Life robs us of ourselves, piece by small piece. What is eventually left is someone else.”

And of course, the author might remind us here, with a wink, that ring was stolen in the first place.