I tried my best to keep in touch. First in icy upstate New York, then later in the high desert of Arizona. I received Scottish newspapers from time to time and I had friends in Glasgow with whom I corresponded irregularly - but the connection with home was unavoidably becoming thin as a membrane. And I didn't want to become one of those typical North American exiles who sip some Scotch and grow gloomy listening to accordion and fiddle music, or who attend replica Highland Games and join assorted Celtic societies.

I once attended a Scottish Gathering in Dallas, out of curiosity. I found it a melancholy affair with slightly lost people trying to come to terms with their expatriate status by joining overseas branches of clans, or buying tartan pin-cushions and souvenir tins of McCowan's Highland Toffee - so much yearning, so much unfulfilled longing. When a well-intentioned, red-haired man called Hector Suarez, of Mexican descent, asked me to join the Clan Lamont Society, I knew there was something out of joint with these assemblies.

Sometimes the occasional drink would warm up the embers of my memories of Glasgow, and what came flowing back were recollections of a big dark city with domineering grey-black tenements and little images scattered in no particular sequence, like flecks in a kaleidoscope. 

There was the Govan Ferry smoking and chugging between Linthouse and Partick; the sooty air of the city that hung to your clothes and your hair and made the inside of your nose black; the mysteriously dank smell that rose out of the subway stations; tramcars clanking through the rain; the matriarchal freemasonry of backyard steamies; the cryptic relics of air-raid shelters ; the marvellous end of sugar-rationing when youngsters could gorge themselves on a technicolour cornucopia of sweeties; the perfume of tobacco being cured in the big factories in Alexandra Parade; the brilliant banter of clippies; leery street-corner bookies; the sight of the Union Jack at half-mast on the damp morning when killer Peter Manuel was hung in Barlinnie jail.

There was also the astonishing discovery around 1961 that Glasgow had a quiet after-hours world where, in certain jazz clubs, you could score marijuana, the very substance you'd only just read about in Jack Kerouac's On the Road. Or you could pilfer from some friend's mother the "diet" pills doctors were prescribing freely to housewives in those days - pure speed that helped women zip through their hoovering and dusting like time was running out - the same pills that kept you and your friends up all night long babbling about the Meaning of Things.

Oh, there was a multitude of little images, smells, tastes, glimpses, inebriations, some clear, others fuzzy, all peculiar to my sense of Glasgow in the mid-1950s and into the 1960s, I still carried around inside me during the 20 years I spent in North America. I loved this rich city. It belonged in my heart, and I in my turn belonged to it.

Was I just a nostalgic fool? I wanted to go home, but I procrastinated nervously. Would Glasgow match my memory? I wanted it to, because I longed for the past to be intact, as one yearns for a comfort zone where nothing ever changes. The same streets, the same old pals in the same flats, the same pubs, the same everything. 

Besides, at the back of my mind was an idea that haunted me, that one day I'd want to write a novel set in Glasgow, about a man returning home after many years of exile.

Although that book wouldn't be written for another 11 years, in 1990 I made a visit. It was the year of the City of Culture - for me the year of culture shock. Where was everything I'd expected to see? I suspected some kind of sorcery had altered the city, and I was strolling through a holograph of a Glasgow that bore no relation to the one I remembered.

Where were the trams and the green and yellow corporation buses? And where in the telephone directory were the names of old school friends? Missing in action, uprooted, emigrated, perhaps dead - who could tell? They were lost to me. And the black tenements I remembered, how had these staunch grim fortresses been transformed into pink and ginger and honey-coloured sandstone extravaganzas? And where were those tantalising closes with tiled walls that almost invited you into the lives of complete strangers - why were so many of these closes concealed behind security doors? And the subway, why didn't it throw up that characteristic smell of burnt oil and damp and decay? And what was this roaring monstrosity slicing the city at St George's Cross, this motorway that ripped through the heart of Glasgow? 

Pubs had developed airs and graces - ferns instead of spittoons. Restaurants were serving something called Scottish cuisine, which invariably seemed to include oatmeal ice-cream and a fish soup by the unappetizing name of cullen skink, and stovies. Stovies? Wasn't that something Maw and Paw Broon ate in the comic strip in the Sunday Post? I never had them at my house. 

Commercial buildings had been facelifted, and delicate architraves and statuary revealed detailed architectural features formerly hidden under black grime. Old warehouses had been transformed into desirable residences. Lofts.

Something serious had happened here. Glasgow was respectable, attention-seeking, fashionable. The mutton pie culture, if it hadn't disappeared entirely, disappeared into the shadows. 

I visited the street in Linthouse where I'd been born and grown up, the tenements had been airbrushed, my old primary school restructured, the local church converted into a community of sheltered houses. My secondary school, a solid Victorian edifice in the east end of the city, had been demolished entirely, the site a field of grass. It wasn't right, something vital had been plundered, it was too damn clean, too . . . douce. It wasn't the city I'd carried inside my mind for 20 years. How could it have changed this much? I felt vaguely estranged in the place of my birth, and a little uneasy.

In 1991 I left the United States to live in Ireland. I made three or four trips a year to Glasgow in the years that followed. I realised after a few visits that many of the changes that had so startled me in 1990 were cosmetic - an underlying Glasgowness hadn't been touched at all. 

There was the same merciless banter, that barbed dry humour I'd never found in any other city. The give and take between vendors and customers at the Barras had never been so sharp, and the quick-witted criticism of highly-paid but hapless players at football matches was as caustic as it had always been.

Unhappily, there were still many areas of the city where the express train of Glasgow's reformation had simply whistled past. Bleak housing schemes where the despair of unemployment was overwhelmingly evident, the graveyard silence of the yards in Clydeside that had cast a pall of depression over the south bank of the Clyde for years - deprivations like these couldn't be disguised by any amount of cosmetic sparkle. 

As people took up residence in modish places like the Merchant City or headed further west down Dumbarton Road, the other Glasgow stumbled along as it had always done - an impecunious cousin on the edge of a ritzy wedding party. 

Something else hadn't changed in Glasgow. One night a couple of years ago my wife and I were attacked in the High Street - it wasn't quite a mugging, since no fiscal demands were made - by a young man who'd walked along behind us repeating the same sing-song spooky incantation, "Ah'm gonny KILL yooooo." I sensed it then, and it was unsettlingly familiar - an encounter with the city's darker edge, where violence suddenly looms out of shadowy doorways.

I remembered Glasgow's old reputation as a brutal city, and realised some of that attitude still prevailed, and probably always would. And I remembered how, as a boy, strange kids would stop you and ask you that scary, inevitable question: "You a Catholic or a Prod?" And while you tried to guess the response that would spare you a hammering, you lived on the edge of tension.

The confrontation with the attacker was brief and injury-free, because a passing taxi-driver stopped to rescue us, then called the police, who seized the assailant and whisked him away. I was tense and distressed, as if I'd been whisked back into those bad moments of childhood.

The taxi-driver took the matter personally, and said: "That kind of thing is just not on in Glasgow. No way."

So there it was. Good and bad, beautiful and shabby, warm-hearted and chilling - the incident contained the distilled essence of the city I loved and would always love.

Like the character in the novel about Glasgow I eventually wrote, The Bad Fire, I'd come home.