'Yes. Who are you?'

'Security Officer U Sit Aye,' he said, and went on to ask when I had entered Burma, and why, and for how long. Then he asked, 'You are a tourist?'

'Yes.'

He thought a moment, tilting his head, narrowing his hooded eyes, and said, 'Then where is your camera?'

'I left it behind,' I said. 'I ran out of film.'

'Yes, we have no film in Burma.' He sighed. 'No foreign exchange.'

As he spoke another train drew up beside the one we were in.

'We will get in that train.'

In the last armed coach of this second train, sitting with a new batch of soldiers, U Sit Aye said he was in charge of railway security; he had three children; he hated the rainy season. He said no more. I assumed he was my escort, and, though I had no idea why we had changed trains, we were on the move, travelling in the direction of Gokteik.

A haggard Burmese man in a woollen cap took a seat across from us and began emptying a filtertip cigarette on to a small square of paper. It was the sort of activity that occupied the foreign residents of Afghanistan hotels, a prelude to filling the empty tube with hashish grains and tobacco. But this man didn't have hashish. His drug, in a small phial, was white powder, which he tapped into the tube, alternating it with layers of tobacco. He stuffed the tube with great care, packing it tight, smoothing and tapping it.

'What's he doing?'

'I do not know,' said U Sit Aye.

The man peered into his cigarette. It was nearly full; he poked it down with a match.

'He's putting something inside.'

'I can see,' said U Sit Aye.

'But it's not ganja.'

'No.'

Now the man was finished. He emptied the last of the powder and threw the phial out of the window.

I said, 'I think it's opium.'

The man looked up and grinned. 'You are right!'

His English, clear as a bell, startled me. U Sit Aye said nothing, and as he was not wearing a uniform the man had no way of knowing he was making an opium cigarette under the nose of a security officer.

'Have a puff,' said the man. He twisted the top and licked the whole cigarette so that it would burn slowly. He offered it to me.

'No thanks.'

He looked surprised. 'Why not?'

'Opium gives me a headache.'

'No! Very good! I like it – ' He winked at U Sit Aye. ' – I like it for nice daydreamings!' He smoked the cigarette to the filter, rolled up his jacket, and put it behind his head. He stretched out on the seat and went to sleep with a smile on his face. He was perfectly composed, the happiest man on that cold rattling train.

U Sit Aye said, 'We don't arrest them unless they have a lot. It's so much trouble. We put the chap in jail. We then send a sample to Rangoon for tests – but his is number three; I can tell by the colour – and after two or three weeks they send the report back. You need a lot of opium for the tests – enough for lots of experiments.'

Towards noon we were in the environs of Gokteik. The mist was heavy and noisy waterfalls splashed down through pipe thickets of green bamboo. We crawled around the upper edges of hills, hooting at each curve, but out the windows there was only the whiteness of mist, shifted by a strong wind to reveal the more intense whiteness of cloud. It was like travelling in a slow plane with the windows open, and I envied the opium-smoker his repose.

'The views are clouded,' said U Sit Aye.

We climbed to nearly 4,000 feet and then began descending into the gorge where, below, boat-shaped wisps of cloud moved quickly across from hillside to hillside and other lengths of vapour depended in the gorge with only the barest motion, like veils of threadbare silk. The viaduct, a monster of silver geometry in all the ragged rock and jungle, came into view and then slipped behind an outcrop of rock. It appeared again at intervals, growing larger, less silver, more imposing. Its presence there was bizarre, this manmade thing in so remote a place, competing with the grandeur of the enormous gorge and yet seeming more grand than its surroundings, which were hardly negligible – the water rushing through the girder legs and falling on the tops of trees, the flights of birds through the swirling clouds and the blackness of the tunnels beyond the viaduct. We approached it slowly, stopping briefly at Gokteik Station, where hill people, tattooed Shans and straggling Chinese, had taken up residence in unused railway cars – freight cars and sheds. They came to the doors to watch the Lashio Mail go past.

There were wincing sentries at the entrance to the viaduct with rifles on their shoulders; the wind blew through their wall-less shelters and the drizzle continued.

I asked U Sit Aye if I could hang out the window. He said it was all right with him, 'but don't fall.' The train wheels banged on the steel spans and the plunging water roared the birds out of their nests a thousand feet down. The long delay in the cold had depressed me, and the journey had been unremarkable, but this lifted my spirits, crossing the long bridge in the rain, from one steep hill to another, over a jungly deepness, bursting with a river to which the monsoon had given a hectoring voice, and the engine whistling again and again, the echo carrying down the gorge to China.

The tunnels began, and they were cavernous, smelling of bat shit and sodden plants, with just enough light to illuminate the water rushing down the walls and the odd night-blooming flowers growing amid fountains of creepers and leaves in the twisted stone. When we emerged from the last tunnel we were far from the Gokteik Viaduct, and Naung-Peng, an hour more of steady travelling, was the end of the line for me. This was a collection of wooden shacks and grass-roofed shelters. The 'canteen' Tony had told me about was one of these grass-roofed huts: inside was a long table with tureens of green and yellow stew, and Burmese, thinly clad for such a cold place, were warming themselves beside cauldrons of rice bubbling over braziers. It looked like the field kitchen of some Mongolian tribe retreating after a terrible battle: the cooks were old Chinese women with black teeth, and the eaters were that mixed breed of people with a salad of genes drawn from China and Burma, whose only racial clue is their dress, sarong or trousers, parasol coolie hat or woollen cap, damp and shapeless as a mitten. The cooks ladled the stews on to large palm leaves and plopped down a fistful of rice; this the travellers ate with cups of hot weak tea. The rain beat on the roof and crackled on the mud outside, and Burmese hurried to the train with chickens bound so tightly in feather bundles, they looked like a peculiar kind of native handicraft. I bought a two-cent cigar, found a stool near a brazier, and sat and smoked until the next train came.

The train I had taken to Naung-Peng didn't leave for Lashio until the 'down' train from Lashio arrived. Then the escort from Maymyo and the more heavily armed escort from Lashio changed trains in order to return to the places they had set out from that morning. Each train, I noticed, had an armoured van coupled just behind the engine; this was a steel box with gun slits, simplified almost to crudity, like a child's drawing of a tank, but it was empty because all the soldiers were at the end of the train, nine coaches away. How they would fight their way, under fire, eighty yards up the train during a raid, I do not know, nor did U Sit Aye supply an explanation. It was clear why the soldiers didn't travel in the iron armoured van: it was a cruelly uncomfortable thing, and very dark since the gun slits were so small.

The return to Maymyo, downhill most of the way, was quick, and there was a continuous intake of food at small stations. U Sit Aye explained that the soldiers wired ahead for the food, and it was true, for at the smallest station a boy would rush up to the train as soon as it drew in, and with a bow this child with rain on his face would present a parcel of food at the door of the soldiers' coach. Nearer to Maymyo they wired ahead for flowers, so when we arrived each soldier stepped out with curry stains on his shirt, a plug of betel in his mouth, and a bouquet of flowers, which he clutched with greater care than his rifle.