The shamans also believed in 'pegging' the earth. This ritual, which was adopted by Buddhist yogis, was employed to control the earth and render it submissive. The ndashung that marked the tops of holy mountains were to bind the earth and spirit powers, taming them through penetration. The mountains themselves are said to peg the earth like nails or phurbas, ritual daggers, piercing and securing it. On a human level, the chortens, stone monuments, I had seen upon entering Amdo were like symbolic mountains suppressing the demonic forces beneath them.

The other major pre-Buddhist religious influence on the Amdo nomads was the Bon religion. Even after Buddhism had replaced it, it still maintained a hold on people in areas as far away as Amdo, which had always enjoyed strong separatist tendencies, especially among the nomads.

The Bonpos also believed in taming and placating the spiritual powers of the environment, gods, demons and spirits. They were devout ritualists who, like the shamanists, sought to keep the old Tibetan gods favourably inclined to human activity. Before the Buddhists transformed the gods into part of the Buddha-dharma, the Bonpos were propitiating them and using their power to maximise human luck. As with the shamans, they focused on the earth-lords and serpent spirits, who controlled the fertility of the land, animals and their own human power, which is why it was so important to placate them.

Another Bon ritual still practised by the nomads included divination, which took many forms. Tsedup had told me that his father would sometimes burn a sockwa, the shoulder blade of a sheep, and foretell future events in the cracks left on its scorched surface.

I had learnt all of these things from Tsedup. I remember him telling me that he had never understood the need for western mountaineers to 'conquer' mountains. For him it was tantamount to hubris. He once saw a documentary about Hillary and Tenzing's ascent of Cho Mo Langma or Mount Everest, as it is called in the West. As they reached the peak, Hillary laid claim to his defeated giant with the arrogance of a big-game hunter, while Tenzing humbly gave thanks to the mountain spirit. A mountain may be tamed and worshipped, but never conquered. Even then, Tsedup's reaction to that TV documentary had seemed to me like a lesson in ecology.

Now, it was fascinating to be witnessing the propagation of these ancient rites. But as I pondered what I had seen, it struck me that I had had no relationship with the land. I'm sure that if I had grown up in the Scottish Highlands or on a ranch in Wyoming I would at least have felt a oneness with the environment, but perhaps, even then, not in the same way. I was a suburban girl. The land, the subtle transition of the seasons, the smell of the earth and real dirt right down in the skin were strange to me. Apart from the joy of a country walk, I had had no previous experience of belonging to nature. These people belonged to the land and respected it with astounding, to me, reverence. Their understanding of the transient nature of life was intrinsic, acknowledged, respected, digested. It was at the heart of nomadic life, along with the acceptance of the swift and unpredictable passage of life and death.

I learnt not just to look, but to see. As I walked in the grassland the next day, I beheld the indefinable strength and solidity of the omnipresent mountains, which seemed like benevolent ancestors contemplating with amusement the scurrying descendants beneath them. Their sunny slopes betrayed a more sinister aspect and their shadows seemed darker. They held curious forms. To the north, they resembled slumbering figures with hulking shoulders slunk into the pit of the land; their valleys and ridges, flesh folds and backbones rolling over and into each other, settled and still. To the south, they receded in waves, peak after trough, until the last visible tips faded into a dusky blue, leaving us behind in their wake. I had never had a true sense of scale until I came here. How frail the tent appeared against this background. Nothing more than a wind-teased flap of black fabric supported by spidery legs that could scuttle away in an instant.

This was my home.

Six. Visit to the Sky Man

We had been in Machu for almost a month when we were summoned to the police station. It was the moment we had both been dreading. Leaving the country surreptitiously, as Tsedup had, could incur a serious penalty or worse. We had heard of others who had returned and been temporarily imprisoned. We had no idea what to expect. I said a silent prayer the night before that no harm would come to him.

The next morning we pulled into the forecourt of the police station, which was the first building on the tarmac road into town. It was of the usual concrete variety, three storeys high, glass-fronted, with the scarlet and gold emblem of the police force hung above its pillared entrance. The third floor was shielded by a large net curtain and was reserved for karaoke parties. The place breathed boredom. Apart from a builder toiling leisurely in the corner of the yard, there was no one in sight. We got off the bike and I followed Tsedup up the steps into the cool of the entrance. It smelt of dust, and I was surprised and momentarily delighted to see Tashintso. She sat in the dark reception room behind a sheet of glass on which were written various scarlet characters in Chinese and Tibetan. She wore her conscientiously pressed dull green police uniform, and a coquettish smile. 'Cho demo,'' she giggled in greeting, as we took seats in the black plastic armchairs opposite her kiosk. Beside her sat another young woman, identically dressed, who smiled shyly at me from beneath her permed fringe. A pile of paperwork sat neatly at the side of their desks, which were otherwise bare. Tashintso came round from behind the glass partition and said something to Tsedup, then she disappeared out of the door and I could hear the clump of her heavy high-heels down the corridor.

'Will they want to see me?' I asked Tsedup, taking advantage of the last few moments alone. ‘I have no idea what to say.'

'Just leave the talking to me,' he said.

But I wasn't reassured. What if they wanted to see us separately? It was like our interrogation at the High Commission in Delhi all over again, but this time more serious. However, I hadn't realised that I would be excluded from the grilling, simply because no one spoke English. A few minutes later Tashintso returned and signalled for Tsedup to follow her. He left, and I sat chewing my lip and studying a calendar with a picture of a tree in blossom beside a lake. The scene did little to pacify me and I imagined that the young policewoman sitting across from me would confuse the thudding of my heart with the thumping of her rubber stamp on the crisp white sheets before her. The main responsibility of the office appeared to be the endorsing and renewing of identity cards for the local population. She stamped face after face. The blood pulsed in my eardrums. My palms stuck to the chair.

Soon Tashintso returned and put on the kettle to make me a cup of tea. It seemed a ludicrously civil thing to do at the time and I felt slightly more at ease. She beckoned to me to come round the back of the screen into their small section where she drew up a chair for me and then pulled out her knitting from the drawer under her desk. As if this were a signal, the other policewoman stopped her stamping and took up her needles from a stool by her knee. Then Tashintso struck up a conversation with me as the pair of them clicked away. She was fashioning a brown tank top with a rather intricate pattern for her husband, and her partner was putting the finishing touches to a fluffy blue jumper for her baby son. The corridors were silent and Tashintso's sporadic giggling and the relendess tick-tick of the needles echoed down the halls. I wondered in what deep recess Tsedup was cornered and strained my ears for a voice. But I heard nothing, except the twang of a plucked guitar string in the karaoke room upstairs and a gurgle as the kettle began to boil.