We walked solemnly behind Aka Damchu through the wooden archway into the next courtyard holding our prayer scarves in both hands. As we passed through the gate, my father and I watched Tsedup for tips on decorum. Then we glimpsed the boy sitting waiting to receive us on his throne. He couldn't have been more than thirteen years old, but his eyes held the seriousness of a much older man. He wore wine-red robes and a length of fuchsia fabric across one shoulder. In his left hand he methodically counted the beads of his tranger between thumb and forefinger as he surveyed his foreign guests with curiosity. Following Tsedup's lead, we kept our heads lower than his out of respect. We approached him in our small procession, holding out our kadaks. He leant forward, took them from our outstretched hands and placed each one around our necks. This was all performed in total silence. He seemed so isolated, surrounded by monks much older than himself, and I wanted to ask him so many things. Had he forgotten how to be a boy? What was it like to be discovered as a reincarnate, to live your life in the image of someone else? Had he been a monk before they found him or was he living with his family? Did he realise his destiny before that time? Was he happy? But I never had the chance to display my ignorance.

We followed Aka Damchu to the other side of the courtyard, still bent in supplication, taking care not to turn our backs on the lama. Our friend led us into a shrine dedicated to Jarsung. As far as the eye could see there were books, all written by the six Jarsungs of the past, lining the walls. Butter lamps glowed fragrantly in front of an altar containing a row of pictures of the Jarsungs. Tsedup prostrated himself in front of them as I inspected their faces. The first four pictures were drawn in ink and showed old men, one in the amazing cockatoo-shaped yellow hat of the Gelugpa sect of Buddhism. The last two pictures were photographs, and one was of a tiny boy. He looked out of place next to these grand old faces. Tsedup pointed at the child. 'He has written all of these books,' he said. It seemed unlikely to me that a thirteen-year-old boy had achieved such a feat. But then I stopped. Tsedup's comment had revealed to me the true nature of the Tibetans' belief in reincarnation. As far as Tsedup was concerned, Jarsung had been the same Jarsung for hundreds of years; it was only his physical appearance that had changed throughout his various lives. He went on to explain that Jarsung had always been gifted throughout his reincarnations and, true to character, the boy we had met today was famed for being a conscientious and exceptional student.

I was moved by this strange encounter. It was a reminder of the atmosphere of mystery that surrounds Tibet: the unknown, magical and isolated Tibet. Such beliefs have a fascination for us in our logical and largely non-spiritual techno-culture, and the practice of determining the rightful successor to a lama upon his death was mystifying to me. Buddhism teaches that the energy derived from the physical and mental activities of a life will embrace a new life when dissolved by death, and has been fundamental to the Tibetan belief system for centuries. A lama's disciple will often search for years to find his reincarnated spirit, and his journey may take him many thousands of miles. When a likely candidate is located he is set a series of tests. These usually consist of the disciple placing objects that belonged to the late lama in front of the candidate, hidden among ordinary things that did not belong to him. The reincarnate will always select the lama's possessions with uncanny immediacy and a peculiar sense of familiarity. He is then recognised and ordained. It is a great honour for his family.

We took tea with Aka Damchu, who presented us with a framed picture of Lama Jarsung sitting on his golden throne. Then Tsedup, who was increasingly anxious about his father, signalled that we should leave. Dad thanked Aka Damchu for his kindness and we left for the town, but not before we had been offered a personal guided tour of Labrang Monastery that afternoon.

My father and I waited in a cafe while Tsedup played detective. It was a dry, hot day and the sun beat down on the dusty tarmac. He returned some time later with no news, but with a leg of mutton poking out from inside his jacket. Despite his worries for his father, he had had time to visit his uncle. That explained the mutton.

We walked into the main enclave of Labrang Monastery, past the tourists and buses and up an earthy alleyway beside one of the main temple buildings. Tsedup led us up some stone steps to a doorway. At the top, inside the cool shade of a room penetrated by shafts of sunlight, we could see a row of monks prostrating. They began in a standing position then lay full length on the wooden floor, polished smooth by hundreds of years of supplication. Tsedup pointed out his seventy-year-old uncle who, he told us, prostrated here five hundred times a day. He certainly looked fit. Tsedup gestured to him from the door and caught his eye. The old monk squinted at us then shuffled over. When he got to the door and saw Tsedup, he cried out in recognition, showing a row of broken teeth. We followed him to his small wooden house, which smelt musty inside from the soot on the ceiling. We drank tea, and Tsedup and his uncle exchanged news. My father asked if he could take a picture of him and he agreed. He seemed fascinated by the camera, which my father gave him to study, along with his mobile phone. He held them gently, feeling the smoothness of the casings. Through Tsedup, he told us he had never seen a telephone before. My father began to tell him about satellites, at which point he handed it back quickly, saying, 'Be careful with that.'

As we left, Tsedup placed the leg of mutton by his uncle's stove – he had kept it hidden in the monastery for fear of causing offence. It was disrespectful to parade part of a freshly killed animal before the eyes of the compassionate monks to whom we were all sentient beings, even the sheep. Then he stepped outside and told his uncle what he had done. A look of surprise came over the old man's face. 'Meat!' he exclaimed. 'I can't eat that.'

'Oh, yes, you can. It will do you good,' said Tsedup. 'You know you haven't really given it up, so why protest?'

The old man's eyes twinkled and he smiled. 'Thank you,' he said quietly.

That afternoon we met my mother, who told us she had chastised the manager for his treatment of Tsedup the night before. 'Do you understand? He is my son-in-law,' she had protested, pronouncing the words with emphasis and volume. As a child I remembered cringing many a time in the supermarket queue on one of our annual trips to France as she spoke louder and slower in English to a stunned shop assistant, who sat waiting impassively for her to go away. Yet this time she had been really angry: she was mighty when defending her brood. But her outburst had been met with silence. An apology was out of the question.

Still, a tour around the monastery would cheer her up. As the other tourists trailed around in groups we were given the undivided attention of Aka Tenzin and Aka Damchu, and were able to view the rooms quietly. Labrang Monastery was beautiful. The main temple building was vast, dark and cool inside. From the lofty ceiling hundreds of thankas hung like the dense foliage of a forest canopy, into which red and gold columns soared like tree-trunks. Yellow cushions were arranged in rows between the columns for the monks to sit on during prayer. Along the back wall of the room was a series of altars, with displays of unbelievable riches: a golden statue of the Buddha adorned with coral, turquoise, amber and silken kadaks; golden butter lamps, silk flowers, and hundreds of Tibetan books stacked on shelves from floor to ceiling, wrapped in yellow cloth with a small blue, red and gold silk marker hanging from each. Order and precision prevailed, suggesting the care and attention lavished on the monastery. The whole place was a manifestation of the nomads' enduring faith and a clear indication of their wealth, for it had been funded entirely by the donations of nomads from the four corners of Amdo. It felt ancient and precious. Dust turned in the rays of sunlight that pierced the gloom. The familiar, musty scent of Uncle's room was also prevalent here, mixed with the thick, rancid smell of butter burning in the lamps. In the next room monks were chanting their prayers, and the rhythmic resonance of their deep voices boomed through to us in the dank air.