On my first British morning, a dank one like all that followed, I took the tube to Leicester Square and walked up Charing Cross Road. It was surprisingly quiet, the rush hour over and the musty bookstores along Charing Cross not yet open for business.

In five minutes, less, I reached Cambridge Circus, one of those disorienting agglomerations where several London thoroughfares converge and then meander off again. And there it was on the right between Charing Cross Road and Shaftesbury Avenue, a sturdy-looking Edwardian edifice, red brick garnished with beaded stonework.

Naturally, no sign or nameplate identified the place. The Circus is so sensitive a location, its creator has written, that its occupants never allow their taxis to pull up at the entrance. They disembark in front of the ornate theater across the street instead, or at Foyle's bookstore a block north. But I had spent weeks reading and taking notes and poring over detailed street maps. I had also, after a series of transatlantic and domestic faxes resulting in a phone call at a certain time on a certain day, consulted with John le Carre.

So I knew that this was the headquarters of the fictional intelligence service whose varying fortunes are chronicled in le Carre's memorable novels. Named for its location and probably also for its dementia, this was the Circus, home of England's spies. Home, in particular, of one quiet little man in ill-fitting clothes named George Smiley. I knew he was no longer up there on the fifth floor, distractedly polishing his eyeglasses with the end of his tie. Le Carre has sent him into a quiet retirement in coastal Cornwall, and insists he won't write about him anymore. But I wanted to see where he'd been.

George Smiley is le Carre's most indelible character. He dominates four of le Carre's novels (including the very first, 1961's Call for the Dead) and had supporting roles and walk-ons in several more (including the most recent, The Secret Pilgrim). He starred, in the person of Sir Alec Guinness, in two BBC-produced series based on the novels, seen in the States on public television. A very modern sort of spy, Smiley, determinedly nonflamboyant (unlike that earlier model, code-named 007), full of unvoiced doubt about his profession, repeatedly booted by his bosses and abandoned by his faithless wife. The Cold War in all its quiet dread and futility can be tracked through his long, wearying career. This was his red-brick bunker.

Despite all that drama -- no, because of it -- the building turned out to be quite unassuming. The China Travel Service (hmmm) occupied the ground floor and "Office to Let" signs hung in the narrow upper windows. Le Carre had in mind the famously dingy World War II-era headquarters of MI6, the real-life Secret Intelligence Service, back when he was "reconnoitering for my fantasy building," he told me. This one "had some of the same qualities of dilapidation and anonymity." Besides, intelligence headquarters requires a number of satellite buildings housing ancillary services -- forgers, transcribers, that sort of thing. They fit best in polyglot neighborhoods like this one. "A tailor here, a Chinese deli there," le Carre said of the environs. "It was unfashionable and rather characterless. When you think of all the odd people who go in and out of an intelligence building, you see the value of a place where divergent people can converge." The several theatrical tenants of the district added a nice literary grace note, all those box offices and costume shops surrounding the ultimate pretenders. So I'd found the Circus, but was it truly evocative of Smiley? It's been 30 years since he and his creator arrived on the literary scene, and London is not immune to change. In fact, an 11-story high-rise has engulfed the old building, cutting off the view from the fifth floor where the chief of the service and his closest aides obsessively tracked the comings and goings of their counterparts in Moscow.

That heavy, unmarked wooden door tucked between a music store and a Ticketron outlet -- it had to be the entrance to the Circus archives, whence certain key files were purloined during the hunt for the Russian "mole" who'd infiltrated the service. But surely there wasn't a Pizza Hut on the corner when Smiley worked here? Le Carre himself mourned a bit, he told me, as his imagined HQ and its environs began to succumb to developers.

The childlike desire to enter a favorite fictional world outlasts childhood itself, I suppose. Though I've never figured out how to pass through the looking-glass or fly to never-never land, I did fly to England last spring in search of Smiley's London.

The fun was that many of the landmarks were just where the novels said they were. They may not be what le Carre said they were (the "Circus" building has no known connection with intelligence) or have the addresses he assigned them, but most are described with precision. Tracking them down with maps and deduction, skulking inconspicuously past a suspected safe house in the rainy gloom of a London afternoon, made me feel a bit spylike myself. It was a pleasant sensation.

Yet Smiley is already becoming something of a historical figure, fading like the Cold War he fought and the Wall he knew too well. Sometimes, in my week-long quest to visit the sites where he'd identified bodies, foiled moles, shrugged off his triumphs while brooding about his betrayals, I thought I'd found him. I'd stepped into a book. Other times, I was too late.


To le Carre readers, 9 Bywater St. is an address as familiar as 221-B Baker St. Smiley's address, unlike Holmes's, does exist; pilgrims with cameras show up there regularly. The house described in the novels was modeled on that of a literary agent le Carre knew, who may actually have resided (his memory fuzzes on this point) on a different street. But Bywater better suited le Carre's purposes.

"I liked George Smiley living in a cul-de-sac, because it's very hard to maintain surveillance in a cul-de-sac," says the author, who was once reticent about his own long-ago years in British intelligence but now casually acknowledges them. Even the Circus's crack watchers would become too noticeable on a tiny dead-end street. Such lack of protection by his own renders Smiley insecure in his own home, which is regularly penetrated by both friend and foe. For an actual spy, this could prove problematic. For an author, it's a good way to keep plots at a boil. Besides, le Carre calls Smiley "a man condemned to live in a siding"; Bywater was therefore the perfect name. The problem, as the later novels acknowledge, is this riverside neighborhood. It was handy for le Carre, who was living just across the Thames "in unfashionable Battersea" at the time he invented Smiley. Call for the Dead makes ample use of riverfront landmarks, including the elaborately Moorish Battersea Bridge, off which Smiley -- in a rare instance of hands-on violence -- actually shoved a bad guy. Chelsea's modestly arty ambiance suited newlyweds George and Ann. But the district turned expensive and chic in the '70s. Worse, it has since suffered the homogenization that has turned too many of London's "high streets" (English for retail arteries) into ringers for American malls.

Thus, emerging from the tube station at Sloane Square and heading down the King's Road as Smiley so often did, I found everything uncomfortably familiar. Century-old storefronts housed a McDonald's, a Laura Ashley, jeans stores and flashy hair salons, the King's Road Safeway. My spirits lifted at the sight of the sign announcing Bywater Street, then slumped when I beheld a Benetton boutique on Smiley's very corner.

The 37 Georgian town houses that lined Bywater were lovely, with their wrought-iron fencing and pots of ivy. But when I walked toward No. 9 I found trucks, dumpsters and men in work boots clambering over the brick walls. "It's being gutted out," the construction foreman said. "Ceiling's down. All new doors . . ." The place had just been purchased, it seemed, by an upscale London couple -- he's a record producer, she's a solicitor -- who didn't even recognize the significance of 9 Bywater St.

The advantage of Smiley's house being a construction site was access: The foreman walked me up the twisting staircase and through tiny rooms that must have seemed terribly comfy once. But amid the clatter and debris my imagination proved unequal to the task of envisioning a forsaken Smiley cooking his solitary lamb chops. And the landscape outside looked entirely too much like Wisconsin and M. Better to seek Smiley where he was really more in his element -- in the field. I went to Hampstead.

It was a Sunday afternoon, which meant that Londoners bent on recreation were filing resolutely through the Well Walk entrance to Hampstead Heath, a 785-acre preserve of woodland and meadow. The rain was steady, but if they waited for a fair day their muscles might atrophy. So the adults walked terriers and wheeled prams while the kids pedaled bikes and even tried to fly kites on the soggy hilltop. I got odd looks for violating this mass delusion by opening my umbrella.

But then, my purpose was grislier. I walked the muddy gravel path between two rows of lime trees (we'd call them lindens) with mounting excitement because the trail was curving a bit and descending, then rising again. The topography was just as le Carre (who lives a few blocks away when he's in London) described it. The lowest point was the "dip" where, in a rainy pre-dawn in Smiley's People, a police superintendent shone his flashlight on a body wrapped in plastic. "Knew him personally at all, did you, sir?" the cop asked when Smiley arrived to ID the corpse. Smiley did: It was Vladimir, who had served the Circus faithfully for years on both sides of the Iron Curtain and had been shot in the face at close range for his trouble. On that wet morning on Hampstead Heath, Smiley's final confrontation with Soviet intelligence began.

Now, which of these trees was the tree, where Smiley subsequently found the item for which Vladimir was murdered? I knew from the book that the tree was forked and slightly off the path, but that description fitted any number of these trees. And, as a small plaque up the hill recounted, a 1987 hurricane had toppled much of this grove.

But when I saw it, there was no mistaking it: a massive lime tree on the left in the dip. It had the requisite divided trunk and, below the fork, a crevice just deep enough to accommodate the cigarette packet that held a piece of evidence that changed everything.

The crevice was a bit higher up than a person of normal size could reach; Vladimir used a walking stick to stash the pack there and Smiley, retrieving it later, fished it down with a branch. "An important thing to remember about what you call 'dead-drops' and what we call 'dead-letter boxes,' " le Carre explained to me, as if all of us were in the espionage game, "is you never put anything within the reaches of animals or small children."

AFTER A WHILE, I NO LONGER MINDED ALL THE PRECIPITATION, It fitted the bleak world that Smiley inhabited; it felt right.

It was drizzling on the morning I visited St. James's Square, home to prime ministers and other swells and, on the eastern side, to the London Library. This private preserve of a million volumes was founded by Thomas Carlyle in 1841. T.S. Eliot served as its president from 1952 to 1964. Among its many scholar-members was George Smiley, who repaired to its reading room during one of his involuntary retirements to compose a monograph on a baroque German poet. (He loved German poets.)

The reading room was under renovation last spring, closed to the public. But a cooperative librarian took me upstairs to see it -- just in time, before a threadbare quality that had clearly taken years to achieve was to be sacrificed to inappropriate cheerfulness. Old wooden tables, a few red chairs clustered around an electric fire, grungy no-color ceiling and walls about to be painted "glossy white and processed pea" (said the librarian, who seemed to disapprove) -- it was perfect for Smiley. "There are lots of people here that study obscure things," the librarian said, recognizing the type. "Others that sleep."

And it was positively pouring the afternoon I went looking for a safe house in Camden Town, a 19th-century town house that figures prominently in the climax of Tinker, Tailor, Soldier, Spy. It was an important location, though, worth a rain-blurred notebook.

In this safe house one chilly night, Smiley waited in the darkness in his stocking feet, feeling oddly empty, signaling occasionally with a flashlight to his deputy watching outside from the towpath along the Regent's Canal. The man who walked through the door of 5 Lock Gardens, Smiley knew, having baited the trap, would be the long-sought mole.

But was there a 5 Lock Gardens? No such street appeared on my maps. I asked a London friend to search her Ordnance Survey atlas, after which she concluded that Lock Gardens was not only a fictional name but a wholly imagined place. No thoroughfare seemed to jibe with le Carre's description of a crescent whose flat-fronted houses had walled back gardens that ran down to the canal, a crescent that lay south of certain landmarks and north of others. Every candidate failed in some respect. But Camden Town is a funky neighborhood off the tourist track, and even a fruitless search might be agreeable. My friend drove me there, in a car with the steering wheel on the wrong side.

We pulled onto a narrow one-way street called St. Mark's Crescent, which on the map didn't look curved enough to qualify and hadn't the proper geographic relationship to Camden High Street. It did, however, run along the Regent's Canal, which transported goods to the London docks in the 1800s before the railroads supplanted it.

I had a good feeling about St. Mark's Crescent as soon as I saw four flat-fronted stucco houses, painted pink or gray or terra cotta, each with three floors and a basement just as le Carre had written. The street numbers were wrong, but that didn't mean anything much.

Could we see the windows of the northernmost house from the canal? A passerby steered us to a concrete-and-metal staircase at the end of the street; we climbed down into an unexpected scene.

The canal was murky brown and lightly dusted with leaves and twigs; a few ducks paddled along. Small wooden houseboats with names like Katy and Shiralee were tied up along the towpath, with flowerpots on their decks and bicycles lashed to their roofs. Other boats, brighter ones painted red and green, glided by on sightseeing excursions that start from the trendy houseboat community called Little Venice. But except for a determined jogger or two there was scarcely anyone in sight and no sounds of tourist revelry from the tour boats. Maybe the rain had muffled everything -- or maybe I couldn't hear much over the accordionist. For, underneath an arched bridge, a man in a wintry knitted cap was pumping out a mournful multicultural repertoire that included "Greensleeves," "Come Back to Sorrento" and -- cross my heart -- the Israeli national anthem, "Hatikvah."

From this strange spot, Smiley's Watsonish sidekick Peter Guillam could easily have seen a flashlight signal from the rear of the white stucco house, raced up the stairway and vaulted the gate just as described. The railroad trestle Guillam saw was clearly visible downstream. This must have been the place le Carre had in mind for Lock Gardens, I thought. He confirmed it next day on the phone.

SUCH CONTACT IS NOT EASILY ARRANGED. To get to le Carre, who suffers journalists primarily when he has a new novel to promote and not gladly even then, I'd called his literary agent in New York. She forwarded my written request by fax. I'd received, after some back and forth, a fax number in Cornwall with which to contact him upon my arrival. It turned out to be incorrect by a digit, necessitating another flurry of transatlantic phoning. Finally, it was arranged that I stand by in my hotel to receive his call at 5 p.m., when he was finished working. He could call me; I could not call le Carre.

When we finally connected, though, he was charming and expansive. He didn't seem to find it stupid or even odd that I was ignoring sights like Buckingham Palace in order to find safe houses; he actually helped. And he laughed when I told him about the accordionist. "Ah," he said. "A watcher."

It's true -- in the process of immersing oneself in spy novels, one can get spooked and paranoid. I'd suspected the accordionist myself. And the hunched-over elderly lady who walked past scattering crumbs for pigeons, whom might she be working for?

In fact, once, prowling through the posh neighborhood east of Hyde Park called Mayfair, a sector Smiley frequented, I knew for certain I was under surveillance. It happened in Grosvenor Square, where the ugliest building for many blocks proved, naturally, to be the U.S. Embassy.

I was looking for the long brick building Smiley visited in The Honourable Schoolboy, its doorways covered by wrought-iron grilles decorated with gilded feathers. I found it on the north side of the square.

In the novel it is officially the Legal Advisor's Annexe, a front for the CIA ("the Cousins," as American spies are known in the Circus). In reality it served as Ike's headquarters for several months during the war (according to a plaque) and was now -- well, what? The presence of security cameras and too many broad-shouldered gentlemen with short haircuts indicated a government building. But when I inquired at the entrance ("Threat Condition: Alpha," a mysterious sign announced), the guard muttered only that the place was called "Headquarters."

Then, lingering by the grilled doorways taking notes, I noticed the same two gentlemen in short haircuts walk by for the second time. When they approached, I noticed too that they were wearing shoulder holsters and carrying radios. "You're wondering what I'm doing," I volunteered.

"Yes, ma'am." Flat Cousinlike accents. I explained about Smiley, of whom they had clearly never heard.

Would I mind coming inside to "clear this up?" they wondered.

Mind? Penetrate "Headquarters"? Possibly chat with actual Cousins? Not at all.

Sadly, the uniformed Marine who met us at the entrance looked dismayed at my appearance and more dismayed at my press card. "I told you to ask her what she was doing, not bring her in," he snarled at my escorts. I was more than free to go.

Still, the closer I felt to Smiley as I tracked his haunts, the more I adopted his watchfulness. From long habit, he noticed every vehicle parked along Bywater Street, and which of them sported suspicious antennas or mirrors. He tucked splinters into his doorway to alert him in the event someone had stolen into his house. His interrogations, during which he seemed half asleep, barely listening, while of course missing nothing, were legendary. Perhaps the pleasure of seeing human qualities (i.e., Smiley's brainpower) prevail, in an era when we all felt the world to be at the mercy of its wayward technology, is one of the reasons we love him.

At any rate, I was sure there was some scheme afoot on the day I went to Lexham Gardens in Kensington. The Circus kept another safe house here, a shabby two-room flat where Smiley extracted a key bit of information from his colleague Toby Esterhase during the mole hunt. It was a time when no one's loyalties were certain.

About safe houses. "In the ethic of agent-running, if it's done well, your prime concern is the agent, the joe," le Carre explained. He invented much of this odd spy talk, scattering terms like joes and lamplighters and scalphunters through his books. Now, I've been told, the spies themselves have adopted his jargon.

In a safe house, le Carre went on, the joe is supposed to be able to let his hair down, bitch about his lot, confide in his handler. The place and its atmosphere are important, therefore. "Is he comfortable? Is he embarrassed? Does he feel conspicuous? Is he at ease?" le Carre said. "The constant search is for someplace that feels cozy."

Lexham Gardens felt cozy. A secluded Victorian square, built around a fenced garden where pale roses and lurid snapdragons bloomed, it was delightfully quiet. Yet it had plenty of exits and entrances to accommodate a nervous joe and his babysitters. Most important, many of the large houses around the square had been converted into apartment buildings, as evidenced by the multiple doorbells. "In an old mansion with perhaps 20 flats, you can have almost countless people coming and going," the author lectured. "It gives assurance and anonymity to the people meeting there."

I would not have known which of these gray-brown brick houses contained the Circus's two rented rooms; Tinker, Tailor doesn't specify. But le Carre had told me: No. 88, at the west end of the square. His stepmother once had a flat here.

Eyeing No. 88 from across the street, I saw that it was, not accidentally, perfectly unremarkable. It wasn't gussied up like the building next door, with its freshly painted trim, or as decrepit as several others on the block. It had eight doorbells. The Circus flat faced front (Smiley kept peering through the curtains trying to ascertain if someone had followed him), but on which floor? Not the second (which the British call the first), probably, because who would tend the geraniums in the window boxes? Perhaps the third.

It was in the midst of such considerations that a milkman in an open-sided electric cart came coasting quietly along the street. At No. 88, he picked up an empty with a note tucked into the neck and left four fresh bottles, then cruised on.

Well. I'd read too many of le Carre's novels to imagine this a coincidence. Somewhere an agent had taken note of this transaction. He might have been up in the safe house, or in the unmarked blue van at the end of the square, or in the vehicle ostensibly belonging to the Royal Borough of Kensington and Chelsea dog warden. She might have been walking along with a poodle on a leash. But someone was relaying by radio, even now, that it had been done: The drop had been made, the signal sent, the exchange completed.

Smiley was being informed. He was standing by at the Circus, or in Berlin, or even upstairs at 88 Lexham Gardens. A dispatcher (who couldn't believe that this little milquetoast was the mythic spy he'd heard about all those years) was saying, "It's done, sir. Four bottles." Smiley, looking as though he'd far rather be reading German poetry, sounded almost diffident as he gave the order. "Very well," he was probably saying. "Proceed."

Paula Span covers New York for the Style section.