Note to aspiring novelists: “If you are capable of not writing, maybe don’t,” suggested Ellen Feldman, dedicated novelist, closet homebody, and dyed-in-the-wool New Yorker. “There’s so much rejection, so much heartbreak. It’s not a way to make a living,” she added, days before the release of her eighth book, “The Boy Who Loved Anne Frank” (W.W. Norton, 264 pages, $23.95), earlier this month. A work of historical fiction, the novel is about Peter Van Daan, the love interest in Anne’s diary.

Ms. Feldman’s success belies her warnings, though. Her last book, “Lucy” (2003), about FDR’s mistress, gave her widest audience yet, and through a twist of serendipity, her bushy little dog. Twice Lucy followed her home from a jog in Amagansett, where she and her husband spend weekends, and twice Ms. Feldman called the number on the dog tag and returned her. The second time, proving that life really does imitate “Sex and the City,” the owners gave her the affectionate creature.

On a recent Sunday afternoon, Ms. Feldman sipped from an enormous mug of coffee while Lucy made a go at sleeping in her lap. The fact that it was the weekend meant Ms. Feldman could relax in her stately Upper East Side apartment, which looks out onto Spanish Harlem, a cluster of museums, and a scrap of Central Park. Every weekday the writer can be found working in the New York Society Library until the librarians throw her out. “I’m not disciplined, but when the writing is going badly, you’re afraid to leave it. When it’s going well, who wants to leave it?”

Ms. Feldman grew up in Elizabeth, N.J., wanting to be a New Yorker from the start. After college, about 35 years ago, she moved to the Upper East Side and, save for a stint on the Upper West Side, has lived there ever since.

To support herself as a writer in her green years, she wrote seven novels under a pseudonym, books she doesn’t like to discuss, as they’re “sillier than I like to think about.” Next came a series of novels about contemporary women, before she came to “Lucy,” her first attempt at historical fiction. She loved the genre from the start, probably because she had majored in history in college and later completed all the courses for a PhD in history, though she never earned the degree. In historical fiction, she said, “I’m dealing with issues that I’m interested in or things that happened to me, but looking at them through the prism of somebody else’s experience. I think that allows me to be a little more honest about them.”

Fiction is often described as an elaborate lie; it’s appropriate, then, that dreaming up “The Boy Who Loved Anne Frank” began with a lie, inadvertent though it was. In 1994 Ms. Feldman visited the Anne Frank House in Amsterdam, where she happened to learn that no records existed telling what happened to Peter in the concentration camps. Immediately, a story took seed in her fertile mind. What would have happened if Peter had made his way to America? What kind of adult would he have become, and how would he have dealt with his horrific past?

The docent was wrong, though: Red Cross records show that Peter did die in the Holocaust. When Ms. Feldman, researching the book a few years later, found out, she was heartbroken that Peter had died, and nervous about the future of her book. That didn’t stop her from going ahead with the novel, though the thought of offending readers with the fallacy terrified her – prompting her to add a hearty disclaimer in the acknowledgements. Her plea to readers reveals the extent to which her characters become real in her mind. “All I can say, and this is not a defense, but I love Peter. I have come to love him,” she said.

She returned to Amsterdam in 2003 to learn more about the people Peter knew in his too-brief life, and to her surprise, found it difficult to learn much. “At the Anne Frank House, they’re kind of keepers of the flame,” she said. “They’re very protective.” They did agree to escort her into a garden that’s closed to the public.” We stood there – there was the chestnut tree that Anne talks about – and I started to cry, as anyone would.”

New York turned out to be a much better resource for her book, partly because of its residents’ compulsive book lending. Someone she had mentioned the project to handed her a privately published memoir by a man who had survived a Hungarian concentration camp. “He came to this country, married a gentile woman, and had children,” she said. “He told no one he was Jewish. Thirty-five years after he had married her, he took his wife back to Hungary, to the concentration camp, and said, ‘Dear, I have something to tell you.'”

This and other stories of reinvention intrigued Ms. Feldman. In her book, she wanted to move past Anne Frank and the Holocaust and consider the process of beginning a new life in America. She created a Peter who blocked off his months in hiding and rejected his Jewish past, fled to New Jersey, and became a successful businessman. Inevitably, though, his history would haunt him. “If you try to deny the past that has affected you so deeply, you push it down here and it pops up there. You have to confront it in some way. It’s always going to be there.”

Ms. Feldman’s greatest difficulty was not staying true to the facts; it was creating a Peter that was authentic – and male. “I’m very much aware that I don’t know how men talk when I’m not there. The closest I’ve ever gotten to it is when I run around the reservoir and I hear men talking. But if they’re young men, they’re faster than I am, so I never hear more than a few sentences!

“Male writers are rarely afraid to write women,” she added. “They just wade right in. Women are very frightened of writing men.”

Her original Peter was a bit of a brute, until she realized that, though considered an anti-intellectual, he was far better educated than most people in the modern day. After revamping Peter, she showed the manuscript to her husband, a psychiatrist.” He said, ‘You were worried about a man? You got a man.'”

Peter and Ms. Feldman are alike in at least one way: They both share a certain peace about them, a reserved humility. Much of her life is lived calmly, whether it’s at home or in the library; she does her best to avoid the crowds endemic to New York. Going out to an “it” restaurant and waiting three hours at the bar is a no-no; better to dine in the solemnity of a private club or at home with her husband. On occasion the couple will exercise their palates over a slow, spacious meal at Le Bernadin – but, of course, there’s nothing crowded about that.

Even so, at times she feeds off the city’s human clutter. “There’s something about living in this city that fuels the writing process,” she said. “I need the people and the traffic.” When, every few months, she craves a dose of claustrophobia, she crosses the park to Zabar’s, possibly the most crowded place in New York outside of Times Square on New Year’s Eve. At Eli’s original emporium, she goes wild and buys out the store. “A woman once said to me I’m an Upper West Sider living on the East Side,” she said, and something in her voice indicated she accepts it, or maybe that it really doesn’t matter.