In a small den filled with books, mementos of a legendary writing career and the requisite command-and-control center (telephone, computer, fax and copy machine), Herbert Mitgang sips on a sherry and offers the secret of his success: "Poverty and idealism," he says with a delightful smile. Ah, so that's it -- that's how Herbert Mitgang has managed to write 14 works of nonfiction and criticism, four novels and a play while until recently working full time as one of the most-respected writers on the venerable New York Times.

The Free Press has just published Mitgang's 19th book, Once Upon a Time in New York: Franklin Roosevelt, Jimmy Walker and the Last Battle of the Jazz Age, a wistful yet bracing amalgam of journalism, political science, sociology and drama. As the title suggests, Mitgang takes a forgotten political feud from the last century and turns it into an uproarious and enlightening tale of New York in the final years of the Roaring '20s and the first years of the Great Depression. The secrets of Mitgang's success might be poverty and idealism, but readers of Once Upon a Time, or any of the writer's works, will soon realize that he backs up such attributes with the authority of a historian, the insight of a journalist, the flair of a born storyteller and the charm of a man in love with his city and its history.

Mitgang works in a small room with a big northern view of Manhattan, facing that part of the island -- East Harlem -- in which he was born 80 years ago, in Fiorello LaGuardia's old congressional district. His Upper East Side apartment, appropriately enough, is in the same neighborhood to which his latest subject, Jimmy Walker, returned every night (well, the philandering mayor was known to spend the night in other places as well) after hours of soaking up New York's nightlife.

On the wall of his den, to Mitgang's left as he writes at his desk, is a 30-year-old picture of the author and Dwight Eisenhower on the beaches of Normandy. Mitgang, during a short stint away from print, was the producer of the legendary CBS documentary D-Day Plus Twenty Years, which aired in the spring of 1964 and featured the personal reminiscences of D-Day's commanding officer. Mitgang himself covered World War II in Europe for Stars and Stripes, and he has bound volumes of that classic newspaper on his bookshelves. Adjacent to the shelves is a framed yellow Star of David, which the Jews of Europe were forced to wear under Nazi rule.

Mitgang's military journalism helped land him a job at the Times in 1945, and, except for his three-plus years at CBS, he was a Timesman for life. He served on the paper's editorial board, edited the paper's drama section, and wrote book reviews and editorials, all the while churning out a lifetime's worth of history and fiction. Actually, Mitgang's day job might help explain his extraordinary literary output. In print journalism, he notes, his task was summed up in a phrase: "How many words do you want and when do you need them?" Those with writer's block need not apply.

His career as a journalist has won him the plaudits of readers and colleagues -- after retiring from the Times in the early 1990s, he was presented with the George Polk Award for his life's work. The award, named in honor of a foreign correspondent killed in the line of duty almost a half-century ago, cited Mitgang's work on behalf of civil rights, court reform, gun control and copyright reform, among other causes. He was praised for having "championed the cause of liberalism vs. dogmatism, freedom of thought and speech vs. censorship of any kind."

Not a bad way to be remembered. Still, Mitgang confesses that for all the memorable stories and reviews he has written for the Times and other newspapers, there's nothing quite like having his work between hard covers.

"To me, a book is still a book," he says, emphasizing the last word with a reverence common among journalists who yearn to explore something more than the headline of the moment. "You can have a pile of your old newspaper clippings, but that's tomorrow's fish wrapping. Somehow, a book has a life."

With the same thought in mind -- something more permanent than a newspaper clipping -- Mitgang made a foray into the theater world in the late '70s, writing a one-man play, Mister Lincoln, that became the first Lincoln play to be performed at Ford's Theater, where Lincoln was shot. The play eventually made it to Broadway in 1980 was taped for television, and continues to be put on in theaters around the world.

Mitgang's new book came about unexpectedly, and not without some resistance on the author's part. The idea was not his -- two years ago, he took a telephone call from Bruce Nichols, a senior editor at the Free Press, who suggested that the scandals that brought down New York Mayor Jimmy Walker in 1932 deserved a new look. Nichols suspected Mitgang might be the man for the job, as Mitgang had written a critically acclaimed biography of the man who investigated Walker's City Hall, Judge Samuel Seabury (The Man Who Rode the Tiger, Fordham Univ. Press). Nichols had also read an essay Mitgang had written about Seabury in a journal published by the Society of American Historians. So Nichols made his pitch to a reluctant Mitgang. "I didn't know whether I wanted to undertake it because I was in the midst of some other stuff, trying to write another play and another novel," the writer says. Typically, Mitgang was turning out reviews and criticism for several newspapers in addition to the Times.

Still, he didn't say no. Instead, he went on an expedition to the famous Strand Book Store in the East Village, trolling the store's shelves in search of a copy of the published papers of Franklin Roosevelt, who was governor of New York at the time the Walker scandals broke. Roosevelt was forced to deal with Walker and the mayor's allies in Tammany Hall at the exact moment when he was preparing to run for the presidency in 1932 -- an unenviable position, to say the least.

Mitgang found the volume he was looking for, and began glancing through the collection of speeches and correspondence. "I got so excited," the one-time war correspondent recalls. "And I suddenly began to envy anybody who had a chance to write about Roosevelt. I started reading this stuff and said, ˜Hey this guy is as radical as Lincoln, maybe even more so.' " That's high praise coming from Mitgang, for in addition to his journalism, fiction and popular history, he is a Lincoln scholar, the author of three books about Lincoln and editor of a collection of letters of another Lincoln biographer, Carl Sandburg.

He was particularly moved by a Roosevelt speech in which the president called for a law declaring that "the labor of human beings is not a commodity or an article of commerce."

"Wow!" Mitgang exclaims. "Can you imagine any of today's presidential candidates in either party having the guts to say that? Roosevelt's words reminded me of a similar statement by Lincoln in his first message to Congress: ˜Labor is the superior of capital and deserves much the higher consideration.' "

He quickly grasped the possibilities that his prospective editor, Bruce Nichols, had seen all along. The time, the place... and the characters! In the battle between Jimmy Walker and Franklin Roosevelt, Mitgang glimpsed the politics of the old, corrupt machine giving way to the politics of social and political reform. Indeed, he concluded that the period could be seen as "the start of the third American Revolution -- after the War of Independence and the Civil War."

And so he put aside the play and the novel. Building on the background of a corrupt but exciting New York City in an era of wonderful nonsense, he reconstructed the Seabury investigation and, finally, the confrontation between Roosevelt, thought of as a lightweight, and the enormously popular Walker. Though a scrupulous researcher, Mitgang writes like a novelist, and he makes highly effective use of the dramatic plot lines and fascinating characters provided by history.

On the day Herbert Mitgang recounts to his visitor the genesis of Once Upon a Time, two fresh clips from the previous day's New York Times lie on his desk, next to his computer. Though he officially retired as a Times staffer in 1992, Mitgang's byline not only still appears in the newspaper's pages, but, thanks to the magic of pre-packaged obituaries, continues to grace page 1. On December 14, he shared a front-page byline on the obituary of Joseph Heller, written several years ago and freshened up by Mitgang's byline partner. Deeper inside that day's paper was a story Mitgang had written about a political-medical controversy, covering speculation that George Washington may have been the victim of 18th-century medical malpractice as he lay on his deathbed.

When the science editor of the Times asked Mitgang if he would work on the Washington story, Mitgang replied, "˜I don't know a damn thing about Washington. I'm a Lincoln expert.' " The editor, with tongue only partially in cheek, parried: "Well, Lincoln's a president, and the other guy's a president." A journalist, of course, can and must be capable of telling a tale about any subject, unlike a writer of history books. As Mitgang points out, "It gets back to the old story: ˜How many words do you need and when do you need them?' " And so, he laughs, in the December 14 edition of the Times, "suddenly this retired guy had two stories in the paper."

In researching the story, Mitgang's first call was to another legendary New York writer, James Thomas Flexner, a white-bearded fixture in Manhattan's Century Club and the author of a four-volume biography of the nation's first president. (Mitgang refers to the 91-year-old Flexner as "Jimmy" and notes that at the Century Club, there's a small couch reserved for Flexner so he can take a midday nap in the club's old dining room.) "So I called up Flexner and interviewed him on the phone about this controversy, and he said, ˜I have it all in my books!' " Mitgang left his apartment, went around the corner to the library at Marymount Manhattan College, found Flexner's biography, "and I became a one-day Washington expert."

Not all journalists can, or wish to, make the transition to amateur historian. But Mitgang wears both hats with aplomb, and is as demanding of nonfiction as any academic. "I've always been a big believer, as an amateur historian, in going as much as possible to original sources," he says. "When I pick up a book, I turn to the back, and I ask, ˜Is this author quoting other authors' books, or is he or she going back to the scene, going back to contemporary sources.' " In Once Upon a Time in New York, Mitgang drew extensively on contemporaneous newspaper accounts of Jimmy Walker's travails and his politically fatal duel with Franklin Roosevelt. But, thanks to his long career as a journalist and historian, he was also able to draw on interviews he did years before with some of the principals in Judge Seabury's investigation, as well as other early 20th-century personages, now deceased, including Walter Lippman, Eleanor Roosevelt, Robert Moses, Felix Frankfurter and Marie LaGuardia (the onetime mayor's wife).

Indeed, over the years Mitgang has been such a prodigious researcher that he is literally a one-man primary source. His papers are already collected and available at the New York Public Library.

Like any storyteller with a sense of history, Mitgang knows that research and in-person observation can make a story come alive, and, just as important, reveal the past to be what it is -- a time not so long ago. Well aware of history's power to make itself felt, the writer tells a story: he and his wife once traveled to Maine to meet the aging descendant of Lincoln's favorite newspaper reporter, a man named Noah Brooks. The old man greeted Mitgang with the words: "Shake the hand that shook the hand of Noah Brooks, who shook the hand of Lincoln."

Which makes a handshake from Herbert Mitgang all the more memorable.

Golway is city editor at the New York Observer and author of the forthcoming For the Cause of Liberty (S&S), a history of Irish nationalism.