Marshall L. Michel III -- former Air Force combat pilot, former NATO war planner, former happy man -- can pinpoint the precise moment when he was transformed from a convivial ex-fighter jock to an obsessive avenger.

While on a business trip to Washington from his Brussels home, Michel returned to the Key Bridge Marriott late on the afternoon of Jan. 29 to find a fax from his Russian wife of five months, Lena Prokhorova. Between the salutatory "I have to tell you something extremely urgent and important" to the closing "please forgive me," Prokhorova lowered the boom:

"I was not in love with you, but I liked you a lot. . . . But as regards the deep and intricate art of living together, it turned out to be so, so difficult. My understanding is that in terms of personalities, mentality and values we are as different as two educated and intelligent people can conceivably be."

Prokhorova, a 40-year-old beauty with a PhD from St. Petersburg, confessed that she had long been in love with another man, that she had married Michel on the bounce after concluding that her lover would never leave his wife and -- oh fickle Eros! -- that she was now abandoning Michel because the lover had indeed dumped his mate.

As Dear John letters go, the missive was plaintive if hardly unique. Happens every day, if not always by transatlantic fax. But the consequences proved anything but commonplace, sending a titillating jolt through the normally sober -- okay, boring -- bureaucratic world of the European Commission, the powerful executive body that oversees the European Union economic alliance.

For one thing, the Other Man was Michael Emerson, a 55-year-old British diplomat and economist who had long served as the commission's ambassador to Moscow, tending the billions in aid money funneled from rich, uneasy Western Europe to poor, unstable Russia.

Moreover, Michel, 53, proved to be no ordinary Jilted Husband. A retired U.S. Air Force colonel who flew 321 combat sorties in Vietnam, the distraught Michel returned to Brussels as a man on a mission. Prokhorova

had cleared out of their apartment in Woluwe St. Pierre, but in removing her computer files from Michel's Macintosh, she failed to realize that the computer was programmed to save documents every five minutes and tuck away copies in cybernetic safekeeping.

Michel found not only a half-dozen drafts of the Dear John note, but also two curious letters written by Emerson in late January, evidently typed on the Mac so he could use the attached laser printer. The first, to a wealthy St. Petersburg businessman named Ilye Baskin, alluded to "our consulting company" and recommended "Kirghizia gold and silver, to be used as guarantee for a credit." The second, to the Coopers & Lybrand accounting firm, referred to the Baskin partnership and laid out a plan for funneling cash from Moscow through Bankers Trust Corp. in New York to a British account in Jersey and ultimately to "an offshore company in Cyprus."

Another letter -- which was written in Russian and which Michel contends was drafted by Prokhorova to Baskin on Emerson's behalf -- proposed that the partnership president collect $1.6 million in advance and a $30,000 monthly salary.

Within an hour after finding the letters, Michel contacted the commission's fraud office. He also got word to the Belgian police and several newspapers, including this one, providing copies of all relevant documents. Investigations ensued, varying in their degrees of salaciousness. ("I've Lived a Lie, Says Love-Rift Temptress," one British headline reported.)

On Feb. 28 the commission rebuked Emerson for "not strictly conforming" to the ethical standard demanded of Eurocrats, which includes tough restrictions on outside business dealings. Since no money appears to have changed hands, Emerson was allowed to take early retirement even as the investigation continues.

Emerson, reached briefly by phone, declared that "there are certain proceedings underway and it would not be correct to have conversations with the press at the moment."

Prokhorova, consenting to a somewhat longer interview, said of husband Michel: "He wants to take revenge, I believe. He's angry because I've left him. That's quite understandable."

And Michel, who seems compelled to talk as long as a sympathetic ear will listen, said, "Every once in a while I wonder whether I'm obsessing about this. Then, about three days ago, I thought, Of course you are.'

"You know," he added, "a friend of mine told me recently, Marshall, remind me never to make you mad.' "

He sits in the restaurant chair as if he's again in a cockpit: alert, erect, ready to act and react. He has chosen a Brussels bistro called Rick's, a lively watering hole with a "Casablanca" motif and a clientele of English-speaking expats. Perhaps not surprisingly, it's a stone's throw from the apartment where Prokhorova and Emerson have sought refuge. Marshall Michel is throwing stones.

"Everything I'd read about Russian women suggested they look at money and life differently somehow. I thought, well, not Lena, she'll be different. Wrong again," Michel says, nursing a beer. "Right now I have no idea who Lena is. I've always said that was part of the attraction, that I didn't really know who she was and she didn't really know who I was."

Their resumes provide a few clues. He grew up in New Orleans, son of a physician. After graduating from Georgetown University in 1965, Michel joined the Air Force, earned his wings, served three tours in Southeast Asia flying F-4s. He married in 1972, inheriting two stepsons. Climbing through the officer ranks, he made the transition to F-15 fighters and served in various staff jobs, including Israel desk officer at the Pentagon and an air planner at NATO headquarters in Brussels.

It was during the Brussels stint, in the autumn of 1991, that he met Prokhorova. They were table mates at a Harvard Club luncheon. (The topic: Russia. The speaker: Michael Emerson. Small world.) After lunch, the mating continued in what Michel describes as "a brief, one-afternoon affair." He suspected she was a KGB agent and dutifully reported the dalliance to U.S. counterintelligence officials, who shrugged with disinterest. She suspected he was a CIA agent, sent to compromise the wife -- as she was then -- of a prominent Russian diplomat.

"That, frankly speaking, is the whole story of our first meeting," she recalls. "It's a nice joke, which I've heard him telling friends and acquaintances at least a couple dozen times."

Daughter of a Soviet naval officer, she grew up in Vladivostok and St. Petersburg. After studying English, German and philosophy at college, she spent two years in India as a translator for the Soviet trade committee. In the 1980s she spent another five years in Nepal as a translator before finishing her doctorate at Moscow's prestigious Institute of World Economy and International Relations. Her thesis explored "Foreign Policy Issues as Viewed by the European Parliament."

On her curriculum vitae Prokhorova writes, "Personal traits: highly motivated, open, friendly, responsible, achievement-oriented with demonstrated skill of working in a fast-paced, international environment."

Shortly before her liaison with Michel, she had begun working for the European Commission's delegation in Moscow. Her boss was Emerson, an Oxford- and Harvard-educated career diplomat who had helped launch the European monetary system in 1977 and who is described by one British scribe as "an unworldly, monklike figure." As Prokhorova told Michel in her Jan. 29 letter, their relationship over the years "grew into friendship, affection and then love."

She was married. So was Emerson. So was Michel. The American's spouse was first to go. Michel left Brussels in September 1992, retired from the Air Force and settled in Springfield to write a book on air combat over North Vietnam. He and his wife separated in February 1993 and were divorced a year later. He and Prokhorova rendezvoused in London in October 1993 for what he recalls as "a great, wild time." She returned to Moscow and divorced her husband, who now is Russia's ambassador to the European Parliament in Strasbourg, France.

Michel assumed he was the cause of the split. Wrong again. Emerson remained her true love; he also remained married. For a prominent British diplomat, a messy divorce and remarriage to a Russian would have been unseemly, particularly for a man who reportedly aspired to be London's ambassador to the United States. According to Prokhorova's Jan. 29 letter, Barbara Emerson discovered his affair with the younger Russian woman and "demanded that we stop seeing each other, which we did."

Trapped in an apparently hopeless triangle, Prokhorova headed for Washington. She and Michel took up where they had left off in London. Last August they were married in Moscow's Wedding Palace No. 4, in a ceremony followed by a lobster lunch at the Metropole.

Asked why she married a man she claims never to have loved, Prokhorova says: "That's easy, that's clear, although even some of my close friends ask me, too. I wanted to get away. It was so difficult and so hopeless, this long story of my love. Marshall had been very, very good to me. He'd been very nice and very supportive for a long time."

He describes her as "the nicest person I've ever met. The six months we were together was the happiest time of my life. She's really nice, really smart, the kind of person with a strong personality but still a sweetheart."

With her 14-year-old son, the couple settled in Brussels, more or less midway between Moscow and Washington. She became a correspondent for Europa magazine, a periodical published in Russian by the commission's Moscow delegation. Michel worked on his book and, as his business card notes, as an "aviation consultant."

On Jan. 24, Michel made his ill-fated trip to Washington, not realizing that Emerson's five-year tenure in Moscow was up and that he had just moved back to Brussels. Even before his return, he and Prokhorova evidently collaborated in seeking a lucrative business arrangement that would capitalize on his stature in Russia and Western Europe.

Barbara Emerson brought things to a head when she discovered, while browsing through Europa magazine, that the Russian femme fatale was once again living in the same city. Again she asked her husband for assurances that he would never see Prokhorova again. This time, according to the Jan. 29 letter, he balked.

"We both believe that we cannot any longer deceive other people, pretending that we have forgotten everything when in fact we have not," Prokhorova wrote. "We love each other and we want to be together."

Informing her husband by fax, she acknowledges, may seem untoward but "it just happened so fast, it wasn't intentional. I had to let him know as soon as I could and there was no other way."

Michel took it badly, and continues to do so. Perhaps inspired by the ambiance in Rick's, he says Prokhorova's departure hit him "the same way Bogie felt on the railroad platform in Paris in Casablanca.' For the first time in my life I thought, This is a nightmare.' " Unlike Elsa and Victor Laszlo in the movie, however, Prokhorova and Emerson left their laundry in the dryer during their hurried flight from Michel's apartment.

Having blown the whistle to the commission, the cops and the press, he continues to agitate for justice or for vengeance or perhaps just for the restoration of lost love. The Belgian police raided Prokhorova's flat and, at Michel's suggestion, seized her laptop computer in a continuing search for evidence of wrongdoing she insists is not there. Both are writing books about the ordeal.

In early February, husband and wife met at Waterloo Tavern for three hours of tearful recriminations. He says she accused him of "kinky sex habits" and arms-dealing with unsavory foreign regimes, and that she threatened him with a vague allusion to what he interpreted as Russian mafia hit men.

"That's not true," she says. "In some things, he has embellished his stories. . . . He calls himself ambivalent. He says there's a Jekyll and Hyde in him, two people, which is probably true."

After dinner at Rick's, Michel climbs into his Camry with the Virginia tags and Tysons Toyota logo. He slowly drives a visitor past the apartment where his wife and her avowed true love now live, then around the block in vain hopes of seeing her walking the dog.

"It's an ugly story," he says with a nod. "A money-and-power story." CAPTION: Russian Lena Prokhorova, left, dropped her husband, American Marshall Michel, above with Prokhorova, for Briton Michael Emerson, right. Michel's revenge: a campaign that would discredit Emerson and rattle the Brussels diplomatic corps. CAPTION: Lena Prokhorova was first the object of Marshall Michel's affection, and then, after she left him, his scorn.