A garish red neon sign caught the eye of writer Gay Talese one night nine years ago as he and his wife, Nan, were leaving P.J. Clarke's—ironically, the same Manhattan pub where they had gone for their first dinner date in 1957. "He said, 'Let's go up and see what it is,' " recalls Nan. "I said, 'No, why don't you go alone?' And he did. When he came home he told me he was fascinated by it. It didn't surprise me later when he told me that this would be his next book."

The sign, LIVE NUDE MODELS, advertised a massage parlor, and with the impulsive decision to go inside, Gay began a nine-year odyssey through the sexual back alleys of America that would strain his marriage almost to the breaking point—and leave him a multimillionaire. Thy Neighbor's Wife, to be published next month, seven years behind schedule, has already earned Talese some $4 million (including a $2.5 million movie sale) and could well emerge as the most sensational book of the year. With the same reporting precision that he previously applied to the Mafia (Honor Thy Father) and the New York Times (The Kingdom and the Power), Talese has created a revealing portrait of the desires and sexual behavior of American men of his background and generation. "This book is not about marriage," says Talese. "It is about love and lust, about experimentation and male fantasy."

Unlike the work of some New Journalists, Thy Neighbor's Wife is strictly nonfiction: All of the names are real. Though most of the names are unfamiliar, Hugh Hefner gets a chapter of his own, portrayed by Talese as a terminal adolescent "unable to deal with women older than 24." Then there's one other middle-aged man cavorting through massage parlors, nudist camps and free-love communes: a minor character named Gay Talese, 48, whose research on the book has long been grist for leering speculation among his peers in the New York literati. "I don't think people will read the book in the way I intended it to be read," sighs Talese. "Only 30 pages are about me. Ten years from now this will be read as a historical book. The gossip will be forgotten."

Perhaps. Yet during the course of his characteristically thorough and highly personal reporting of the book, Talese himself became a story more than once; besides the usual publishing-luncheon chitchat, there were two much-talked-about magazine articles—the first reporting his escapades in massage parlors he managed for two years, the second revealing that he had slept with one of the women he was interviewing in his townhouse office. Predictably, under the circumstances, even some of his friends thought he and Nan were on the verge of divorce. Yet somehow they have made it through—and they say their marriage now is stronger than ever. "I was under enormous pressure," admits Nan, who walked out for a weekend after Gay agreed to discuss his work in progress with a New York magazine reporter. "I think people did a lot of talking behind our backs, and the publicity was very hurtful to all of us. But I never felt our marriage or his love for me were threatened."

An unabashed double-standard bearer, Talese explains his own infidelity as he explains that of the other men in his book—by postulating that men, unlike women, naturally desire sexual variety. If Nan ever had an affair, Gay says he wouldn't want to know about it—and he doesn't think she has. Nan, 46, a vice-president at Simon & Schuster, who edits writers like Oriana Fallaci and Judith Rossner, went over virtually every page of the manuscript with Gay before he showed it to his own editor at Doubleday. But she refused his invitation to join him at the sexually liberated Sandstone community in California, and even now she accompanies him only with reluctance on his annual summer sojourns at a nude resort. That reticence seems quite appropriate to him. "Respectable women will not pay for sex," he says. "The movie American Gigolo is not true. Lauren Hutton would not pay a man to go to bed with her." For those men who pay for sex, he has only sympathy. "The millions made by porn kings come from lonely men," he says. "When they left the massage parlors where I worked, they were happier. There is tremendous sexual frustration in this country."

The book's subject guarantees controversy, and though most of the reviews aren't in, an opening fusillade has already been fired by New York Times columnist John Leonard in Playboy. "In Thy Neighbor's Wife, nobody seems ever to have graduated from junior high—least of all Talese," writes Leonard, shelling the book as "a pile of anecdotes, stapled together at random." But Talese is prepared for criticism, and his faith in his work is unwavering. "There's a lot of envy in these writers who can't write successfully at book length," he shoots back with a bitter ad hominem. "Leonard is a terrible writer. And he's a man who had an affair and ran off with a friend's wife—and here he is, reviewing Thy Neighbor's Wife."

Those are street-fighting words, and they betray Talese's heritage. Son of an Italian immigrant tailor, young Gaetano grew up in Ocean City, N.J., an Italian outsider in a Methodist town where even the Catholic minority was mostly Irish. A onetime altar boy, Gay attributes his past sexual repression in part to his parochial school upbringing. "Once, in the fifth grade, I was sitting with my hand in my pocket, scratching myself," he recalls. "The nun stopped reading, looked at me and said, 'Take your hand out of your pocket.' " A poor student, Gay had one clear talent—reporting. At 15, he was already writing a column for the weekly Ocean City Sentinel-Ledger. "I was a daydreamer, wondering about people," he says. "Whatever I liked to do, there was no class for."

After majoring in journalism at the University of Alabama, he landed a copyboy job at the New York Times, and—with time out for an Army stint—he was eventually promoted to reporter. Through a friend he was introduced to Nan Ahearn, a pretty young graduate of Manhattanville College of the Sacred Heart. "I had never met anyone like him before," recalls Nan, the daughter of a New York banker. "There was something about him I was attracted to." They dated for two years, and when Gay was in Rome covering the filming of La Dolce Vita, he cabled Nan to join him. They were married in Rome in a civil ceremony, with writer Irwin Shaw as best man.

At the Times Gay earned a reputation as an elegant stylist with a flair for longer features. To develop that forte, he left there in 1965 to write magazine articles and books. He has done well. Even before Thy Neighbor's Wife, he earned a sizable income, enough so that he has gradually bought up the entire East Side brownstone in which he first rented a small bachelor flat.

Having emerged from his decade-long project, Gay has resumed his old lifestyle. Nan continues to spend most nights at home with their daughters—Pamela, 15, and Catherine, 12—while Gay, who longs for conversation after a solitary day at the typewriter, will often be found at Elaine's, a chic local eatery frequented by writer pals like David Halberstam, Michael Arlen and A.E. Hotchner.

How has Thy Neighbor's Wife changed him? He is now "a First Amendment absolutist," he says—utterly opposed to government restrictions on pornography. He also reports feeling more comfortable with his own sexuality, as evidenced by his love of nudism and a new ease in showing affection to male friends. "I can now kiss certain men very naturally," he reports. "I kiss Ben Gazzara on the mouth—it is a Latin thing with us—and I don't worry about being homosexual."

Besides financing his taste for fine clothes (he owns 40 suits), his windfall has barely affected Talese. He likes old, familiar things—his 1958 Olivetti typewriter, his 1957 Triumph sports car and the rambling Victorian summer house that he bought in 1969 in Ocean City, miles away from the fashionable Hamptons. Most important, he prizes his 21-year marriage to Nan and is grateful that she tolerated nine years that might have led other—perhaps most—wives to covet their neighbors' stay-at-home husbands. "People who take risks and are ambitious put themselves on the line," observes Nan. "Nan," says Gay, "is the most attractive, strong, intelligent, wonderful woman, and I've never found anyone on her level. I consider myself very lucky."