After a lifetime of telling stories, of reimagining history both Irish and American in popular novels and nonfiction works (“The Officers’ Wives,” “Liberty!: The American Revolution”), Thomas Fleming has turned his scrutiny to the story of his own family, and the rise and fall of its political fortunes in Jersey City in its heyday.

“Mysteries of My Father” (John Wiley & Sons, 352 pages, $35.99) is the story of his parents’ marriage. But it is also the story of the Irish arrival in America and their stubborn rise to political dominance in northern cities. Mr. Fleming’s nervy father eventually hitched his star to that of the powerful Jersey City mayor, Frank Hague.

The caricature of Frank “I Am the Law!” Hague and his political machine used to be widely known. Just as Chicagoans always were asked about Al Capone when they traveled anywhere else, people from Jersey City were asked about Hague. As a young man in the Navy, Mr. Fleming would try to explain the actual derivation of the “I am the law!” quotation to strangers. But gradually he gave up trying to justify his hometown or its mayor, known more commonly as “the big fellow.”

For generations political scholars have grouped Hague together under an umbrella of “machine bosses,” from New York’s Tammany figures to Boston’s Mayor Curley and Chicago’s original Daley. But Mr. Fleming, who grew up inside Hague’s supposed machinery, experienced it only as a collection of human beings held together by strong organization and what he calls Irish loyalty.

To the young Thomas Fleming, Hague was a flesh-and-blood political animal. He bravely defied the Protestants who had held power in Jersey City before World War I, even as he coopted reformers and brand new women voters with “good government” touches – all while keeping a handsome cut of the remaining illicit businesses for himself. Hague’s own aggrandizement may have accompanied the political rise of his supporters, but there was nothing machinelike or robotic about their allegiance, Mr. Fleming notes. By most accounts, the city roughly worked, if within the “morally gray world of Hudson County politics.”

Mr. Fleming’s parents were a mismatched pair. Teddy Fleming was a rough, fearless Sixth Ward slum kid who made good in the Great War as a lieutenant and war hero at the Argonne. Kitty Dolan was a beautiful “uptown” Irish girl, a cultured kindergarten teacher and daughter of a drunk. However appalled she may have been by Teddy’s street grammar, Kitty saw in him a reformable young man with a promising political career. Teddy soon had the admiring eye of influential Hague men, and later of the big fellow himself.

As time went on, though, Kitty lost tolerance for Hague’s style of politics or for the rowdy election-night parties she was expected to host for people she called “the low brow.” As Teddy Fleming rose to become leader of the Sixth Ward and eventually the city’s sheriff, his need for the social tutoring of his classy wife lessened. According to Mr. Fleming, the couple’s bickering increased along with his father’s time outside the house socializing and fulfilling political favors.

As his father became a more grumpily remote figure, Kitty filled her eldest son’s ear with fierce resentment of her husband – until, by his teenage years, young Thomas Fleming was a pious, bookish mama’s boy waiting to be called to the priesthood. Teddy gruffly advised against it, and soon World War II intervened.

Mr. Fleming could not have told the story of his parents’ families without describing the larger saga of the Irish in America – to “unite the tragic history of a people and the tragic history of family.” But he does both very well. Readers who are won over by his telling will likely forgive Mr. Fleming’s use of made-up dialogue – a sin for a historian – since in this case the talk is not invented out of the air but distilled from decades of the author’s own family lore. Here is Mr. Fleming’s account of his parents’ arranged meeting on the day Teddy Fleming returned from the war in his officer’s uniform and Sam Browne belt:

“Kitty asked the lieutenant if he had gotten to Paris. ‘A few times,’ he said. ‘Nice town.’

‘What did you think of the Louvre?’ she said.

‘The what?’ he said.

‘The Louvre. The national museum.’

‘I skipped it. I spent my money on the Folies Bergere.’ He surprised Kitty by pronouncing ‘Bergere’ correctly. He must have met a few French people.”

The rift between his parents and the very different backgrounds of father and son account for some of the lasting “mysteries” alluded to in Mr. Fleming’s title. The book opens, however, with a dramatic solution to one of them: the recovery of Teddy Fleming’s ring, lost by the author in 1968 on a visit to the site of his father’s heroic ordeal in the Argonne Forest.

Some 30 years later, a French hobbyist discovered the gold and onyx ring while sweeping the famous battlefield with a metal detector. He e-mailed Fleming, who flew to France, where the story of the ring reunion made both French and American news. On the ring was inscribed: “FROM MAYOR FRANK HAGUE TO SHERIFF TEDDY FLEMING 1945.”

Mr. Fleming’s long-delayed story of his parents, Frank Hague, and the “old crowd” is premised by this recovery of the ring, the symbol of his final coming to terms with his father and the life he led. The result, an attempt to “explain to myself and others how fear of Teddy Fleming turned to forgiveness and dislike to admiration,” is as rewarding as it is brave.

Mr. Ward last wrote in these pages on Damon Runyon.