Does the past really teach us the way to go forward? Must the yarn be unraveled to see the threads which make it so? In Derry, the second city of Northern Ireland, the past sits in a courtroom. The past is the subject of judicial scrutiny. But the past is a chimera, a shape-changer, and the job of deconstructing it seems an impossible one. However, that is the task, which the Bloody Sunday Inquiry at Derry's Guildhall has set itself. To look at the events of one day in 1972, when in the aftermath of a civil rights march, the British army shot and killed 14 unarmed civilians. Thirty years have passed, an earlier inquiry was a whitewash, the guardians of memory are older and the little girl in the lemon sundress seated peaceably in the relatives' gallery listens to testament from a time and place beyond her ken.

The press box is ataractic; one journalist rests his feet on the handrail, slouches in his seat and appears to doze. Motes dance in a shaft of sunlight from a stained glass window. The large room surmounted by a pipe organ is filled with the various legal teams and their serried ranks of PC screens. Author Simon Winchester is in the witness box. He's here to tell of the events he witnessed on Bloody Sunday whilst a reporter for Britain's Guardian newspaper. He's soft-spoken, tentative at first, but grows in confidence as the minutes pass. But where exactly was he when a bullet whizzed past his shoulder? Did he go east or west along a particular street? Was the noise he heard machine gun fire or an army helicopter overhead? Here memory must be supported by deduction, surmise, conjecture.

He says he feared that his green Barbour jacket might have made him seem like a member of the IRA and therefore a target. The slouching journalist sniggers. "Yeah," he mutters, "the IRA all went about in Barbour jackets," and then commences to whistle softly through his teeth. The elusive past sheds a few facts, but remains inscrutable. That day in May was just one of Winchester's recent forays into the past. In fact, he could be seen as a man in thrall to the past, both his own and that of the subjects he has chosen to write about. Formerly a crack foreign correspondent (mostly with the Sunday Times and the Guardian), he has always produced books in tandem with his journalistic work. But it was the publication of his runaway bestseller, The Professor and the Madman (HarperCollins, 1998), about the role played by schizophrenic genius William Minor in the compilation of the first Oxford English Dictionary, that brought his book-writing abilities firmly to the fore His new book, The Map That Changed the World (HarperCollins; Forecasts, June 4), was inspired by his childhood passion for ammonites. It details the life and times of William Smith, the 18th-century British founding father of modern geology. A humble surveyor and engineer, the autodidactic Smith discovered that fossils occurred in predictable layers beneath the ground. Extrapolating from this discovery, he was able to show how England's subterranean strata could be accurately mapped. Furthermore, he was acute enough to grasp that his theories questioned the Genesis version of creation and Bishop Ussher's estimate that the world was 5,772 years old. But the man who made Darwin's later work possible was not a gentleman and was without influence where influence counted. His discovery was plagiarized, and it seemed he might go to his grave ruined and bankrupt. Thus, this book, which could be categorized as popular science, comes with the page-turning impetus of a life lived passionately and against the odds. In other words: a classic yarn, which British readers have already made a bestseller.

As befits an inveterate translocator, Winchester is next seen at Cuan, the car ferry terminal for the western Scottish island of Luing, where he lives in a pretty stone cottage. He's standing resplendent in shorts and a many-pocketed vest as a soft rain drifts down. PW has traveled five hours to this meeting place, much of it spent in a tiny two-carriage train, which wound its way at a leisurely pace past bluebell-carpeted woods and brooding corrie lakes. As we wait for the ferry to take us what looks like a wading distance to Luing, we contemplate the high sky, the still water and the waiting island. The placid rural quietude is an invigorating contrast to the stultifying hush of the Derry inquiry a month before.

Winchester's Land Rover, which takes us to the cottage, has an array of travel guides ranged above the glove compartment as if he might at any minute take off for Greenland or France. In fact, he is about to take off. Today is his last full day in the cottage. Tomorrow, he and his young partner, Sophie, travel to the States, to move from a pied-à-terre in Wassaic, N.Y., to a splendid clapboard house on 68 acres of Massachusetts farmland.

There, for the first time ever, Simon Winchester plans to take the idea of rootedness seriously. He's nearly 57, and it's well past time to explore the virtues of the familiar: to find out what the word home really means. As a foreign correspondent, he has been a globetrotter extraordinaire and has lived as many lives as the proverbial cat. In the course of his career, he has covered not only the Northern Ireland conflict but the creation of Bangladesh, the fall of Marcos, the Watergate affair, the Jonestown massacre, the assassination of Sadat, the demise of Pol Pot, the handover of Hong Kong and the Falklands War (during which he was imprisoned by the Argentines on spying charges).

To date, he has been addicted to the dizzying charge travel gives; an everyman waiting for the next train filled with strangers en route to tomorrow. It seems likely, though, that the first journey he made is the key to his wanderlust. When he was born in 1944 in North London, his father was in the army and was captured by the enemy on D-Day. He returned to England in March 1945, and Winchester says ruefully, "I've often thought it must have been quite a strain for my father. He'd had a miserable time in Braunschweig POW Camp. He presumably wanted to come back to a woman who would look after him and be nice and tender. Instead, there was this seven-month-old strapping baby. I was sent off to boarding school in Dorset at the age of five, and I often think that was just my father saying, 'Look, I want to just be with your mother, thank you. And you've already intruded too much into my life. So go away!' "

It's quite evident that Simon Winchester admires self-made men—witness Minor and Smith. He writes of outsiders and autodidacts with empathy and, despite the privileges of a private education, an Oxford degree and a nice accent (not of North London origin), feels he belongs in their ranks.

The combination of his lower middle class, "glacial," home background and his rearing in the company of strangers set him apart from his moneyed, cosseted peer group. He scorns the privileged classes, most especially the British peerage, and defines himself as a "classic meritocrat."

When color blindness put an end to his plans of joining the navy, he went up to Oxford to study geology and at the end of his degree found himself working for an African mining company on the borders of Uganda and the Congo. There, in a tent one night, he opened a book called Coronation Everest, about the 1953 Everest expedition of Hillary and Tenzing. Written by the Times journalist James Morris (who was present on the climb and subsequently became the most internationally respected of travel writers), the book also related the story of Morris's battle to get news of the successful ascent relayed to London in time for the coronation of Queen Elizabeth II. "I read this book," says Winchester with crystalline recall, "and instantly I knew this is what I wanted to do. It was about going on adventures and then telling people back home about those adventures. I wrote to this author James Morris and said I've just read Coronation Everest and basically my question is, 'Can I be you?' " Winchester immediately regretted the letter. Why, he thought, would a famous author be interested in him? But three weeks later, Morris replied with the advice that if Winchester wanted to become an adventurer and writer, he'd best come back to England and find a job on a newspaper. This Winchester achieved in short order, and from his first job with a small local newspaper in Newcastle-upon-Tyne, Morris was a kindly, mentoring presence.

Fast forward seven years: Winchester is hill-climbing in Wales not five miles from Morris's home, and decides at long last to meet his mentor in the flesh. A phone call elicits an immediate invitation to tea. Later, at Morris's house, a bizarre scene unfolds. "I knocked on the door and a woman appeared. I said, 'Hello, I'm Simon Winchester, you must be Mrs. Morris,' and this person said, 'No, I'm James actually.' She said, 'Come in and meet my wife.' I thought this was some strange Welsh joke." Having read about all the manly adventures of James Morris, Winchester still expected to see "a bearded, Yukon Jack shirt—wearing fellow, but in fact, in came Elizabeth Morris with their little girl, Suki, and we all sat having tea. It was an unusual, strained occasion. Nothing was said; this, after all, was Britain." Two days later came a letter apologizing for the awkwardness and explaining Morris's desire to become a woman. (He was about to go to Casablanca for sex-change surgery.) Winchester would know Morris from then on as Jan, and the former writing relationship went on to become a close personal friendship which Winchester values highly.

With his years as an award-winning foreign correspondent behind him, Winchester savors the idea of belonging to a rural American community. It's a long way from Kosovo, but he insists that he was never addicted to the thrill of danger in covering war-torn regions. "I think what I'm addicted to, and I sense as I say this that it can sound awfully phony, but I think it's to knowledge and learning and the telling of the story." If there is a problem, it's "that you get experience overload. When in any one week of your life you pack in more dramatic experiences than someone else might have in a lifetime, you run the risk of dulling your senses and losing your sense of wonder."

But, as it turns out, the writing of nonfiction books comes with its own select mine fields. Academia is suspicious of Fleet Street, with its popular versions of history, and at the early stages of researching The Map That Changed the World Winchester found that Hugh Torrens, an English academic, was already engaged on a lengthy work about William Smith. Torrens was of assistance to Winchester, despite finding it "ridiculous" that a journalist would take on such a project, but later lost his contract with Harvard University Press when American publishing circles got wind of Winchester's imminent book. Simon Winchester finds it in his heart to be sorry. His book, he says, was meant to be the "hors d'oeuvre" to Torrens's "main dish."

These days Winchester is taking stock. In a recent Sunday Timesarticle he's still sniffing suspiciously around the idea of settling down in Massachusetts. "Might this, at last, be the Great Good Place?" he writes. "Or will the siren call of somewhere else sound once again and make this place, and the person I am going there with, be just as temporary as all before?" And the life, until now, has had a headlong, accidental quality. He married his first wife, Judy, in 1966, and they had three sons. But Simon's adventuresome, libidinously charged lifestyle led him to be "promiscuous" and destroyed his marriage. A subsequent fleeting affair produced a daughter. He married again in 1989; eight years later, during the handover of Hong Kong, that marriage also ended.

Now, he is predisposed to unpick the knots of his own ineluctable past; to examine the weave of his life to find a discernible pattern beneath the words. He has been a "light, dispassionate" observer at the events, episodes and wreckages of his life. "This is where I am in my life now," he says. "I'm wondering, is my life something more than just a collection of stories? I feel that somewhere there are feelings I've not felt, sensations I've not experienced, things I may never be able to tell. But at the moment I haven't worked out what those are. This is the biggest piece of investigative journalism yet."