“Do you have to psychoanalyze everything,” asks husband Robert Morgenthau in wife Lucinda Franks’ unrestrained romance memoir about her improbable marriage to the celebrated former Manhattan district attorney.

The answer is a resounding yes, as Franks explains why in 400 pages that enliven readers with insecurities and discernments about her relationships with her mother, her father, her stepchildren, and especially with the man, 27 years her elder, she wed.

Intimate details of the couple’s rapt affection for each other despite the generational divide entice but also overwhelm at times the message of how they navigated the shoals of “a marriage that was never supposed to happen.”

Franks was an apple-cheeked, pot-smoking 26-year-old journalist honed by anti-Vietnam war sentiment when she interviewed the widower Morgenthau in 1973 about the Watergate scandal. He was the patrician U.S. Attorney for New York forced to resign by Richard Nixon early in his presidency.

Morgenthau’s wife had died of breast cancer a year earlier, his heart available for the taking. Even though their first date didn’t occur for months later, Franks admits first impression fascination with his clever demeanor, his intellect and his aristocratic bearing. She observed later, during their courtship, that “he was the kind of man they didn’t make anymore.”

The couple married in 1977 despite disapproval by his four children, who thought the age difference too much and feared gold-digger intentions. Franks and Morgenthau didn’t blink. They went on to prove that a younger woman and a man old enough to be her father from dissimilar backgrounds can attract electricity like opposite poles if their hearts are in sync.

“Timeless: Love, Morgenthau and Me” is a documentary novel that publicly rewinds the nearly four decades of marriage through its exciting, exhausting and distressing times. Franks tells their love story with the precision of an observant journalist who co-won the Pulitzer Prize for national reporting in 1971 for a series of stories about an anti-war radical who died when a nail bomb she was making exploded. A 24-year-old UPI reporter at the time, Franks was the youngest recipient of journalism’s Holy Grail.

With Morgenthau’s backstage influence, Franks next works briefly for the New York Times before becoming a freelance magazine writer and triumphant author. Now 68, she casts her literary hubris secondary to the marriage, to the encouragement of her husband’s career, to seeing their journey through the eyes of endearment.

The unlikely and forever commitment clicked. Franks and Morgenthau went on to have two children of their own, he was elected district attorney an astounding nine times, retiring only four years ago at age 91, earning the reputation as one of the smartest prosecutors around.

“Timeless” is enthusiastically personal to Franks’ beloved “Bob,” a protégé of New York’s political royalty. Morgenthau’s father served as President Franklin D. Roosevelt’s Treasury secretary; his grandfather President Woodrow Wilson’s ambassador to the Ottoman Empire during World War I.

“Light falls upon your exquisite forehead, your extravagant Roman nose,” Franks writes of her husband. “The hand beneath your cheek rumples your lips. I gently place my fingers on your lids and feel the rapid flutter of your eyes. The wings of a hummingbird. Such are the things that make love ache.”

All well and good, but repeatedly Franks tells us far more than we want or care to know about their sexual adventures – he made pancakes in the morning after their initial night together, they get intimate in a hospital bathroom.

She describes waves on a beach (“They rode in like stallions, manes flying, then suddenly broke, spilling over into a million pieces, routed, fooled, disintegrating, their ends a foamy nothingness …) before getting right down to it.

“… My nightgown was streaked with dirt. He wanted to put me in a hot shower, but I shook my head and put my icy hands under his nightshirt. He jumped.

“He scowled but didn’t move a muscle. Did I see a little glint of amusement? We took off our nightclothes, and, with salt on my face, frigid as an ice block, we made love as we never had before.”

Throughout the book, Franks describes conversations and incidents in such incredible dialogue, replete with facial expressions and hand gestures from decades past, that she must have a photographic memory, be one of the most assiduous diarists in literary history or has chosen to take a novelist’s license.

A pixie peacenik with charm, she didn’t lack for male friendship. Actor Robert Redford called her three times in 1975 after she interviewed him about his role as a bookish CIA employee in “Three Days of the Condor.” Nothing came of it. Her destiny was Morgenthau.

There are other, less sensuous rewards for the reader deeper into this richly introspective narrative, including background about her husband’s pursuit of several famous cases, his successes said to have inspired the chief prosecutor’s role played by Adam Schiff in the TV series “Law and Order.”

She notes that Morgenthau, twice an unsuccessful candidate for New York governor, has had a remarkable career, including prosecuting Mark David Chapman, who assassinated John Lennon; Bernie Goetz, the “Subway Vigilante,” and several corporate scoundrels, particularly 1991’s Bank of Credit and Commerce International investigation that Morgenthau described as “the largest bank fraud in world financial history.”

Former Morgenthau-trained assistant district attorneys include New York Gov. Andrew Cuomo, former Gov. Elliot Spitzer, John F. Kennedy Jr., and Supreme Court Justice Sonia Sotomayor.

Franks also peers into the lives of other prominent men and women, including Ronald Reagan, Ariel Sharon, Joyce Carol Oates and particularly Hillary Rodham Clinton. Franks landed the first sit-down interview with her about Bill Clinton’s affair with Monica Lewinsky. Hillary’s claim that Clinton’s infidelity and sex addiction stemmed from his abusive mother caused a national sensation.

The enduring marriage of Morgenthau and Franks is not without its trials — he developed melanoma, she breast cancer — and many arguments. Yet this is an intriguing true love story with adventures, humorous anecdotes and happy endings.

She writes: “I am fortunate to have a husband who allowed me to do this; to talk about the personal life that he has kept so private during his 45 years as a public figure; to divulge the unknown stories behind his major cases; to reveal the intimacies, the foibles, the highs, and the lows of our 36 years together.”

If there is a denouement, it is Franks’ discovery that Morgenthau suffers from post-traumatic stress disorder from his heroic service as a Navy officer in World War II. With that realization, both husband and wife come to a better understanding about his often-stoic treatment of her.

“Word by the millions have been printed about you,” she writes, “but none have revealed your real life, your secret life – that you belong to me.”