He was brought to a blocky tower that loomed over the palace complex. And, looking up at the tower's sheer face, he saw what looked like a fishing rod protruding from one window, with a line dangling from it, high in the air.

He found a broad staircase, and climbed up to an open landing. A man was sitting on a ledge, one leg dangling out over infinity. He was indeed holding a fishing rod. At first he didn't notice Harry.

Harry walked to the ledge. He was on the north side of the Alhambra, and below the wall the land fell away. To the north a glen opened up to reveal a river threading through a quilt of terraces, orchards and gardens. The city itself was laid out before him. The sun was setting now, and its light, low and turned red by the dusty air, painted the domes and towers pink. Looking beyond the city to the south he made out the angular peaks of the Sierra Nevada. In the shadows below the icecaps he saw the sparks of fires; he would learn that these were the fires of ice collectors, who travelled up into the mountains with their mules every afternoon, and clambered back down in the night. Thus the ice of the mountains cooled the palace of the emir all summer. A subtle mist rose from that river to the north, and the sounds seemed enhanced, so that Harry could make out a child's laughter, the chime of bells, a guitar's gentle music, and, from the heart of the city, the first wail of a muezzin.

As he stared, wide-eyed as a child, the man on the ledge smiled at him. He was perhaps fifty, with a broad weather-beaten face.

Harry, a little embarrassed, approached him. 'You're fishing,' he said.

'Indeed I am, with a hook baited with flies. I am angling for swallows. Fishing in the sky,' said Abdul Ibn Ibrahim, and his grin widened.

Abdul's office was a pretty room with a fine view, cluttered with scrolls and books and charts and heaps of scribbled-on parchment.

Here Harry and Abdul talked briefly of their lives.

They had little in common, Harry thought. Nearly twice Harry's age, Abdul lived alone. For most of his life he had made a living at sea, a career recorded in his leathery face. But he was a navigator, perhaps strictly an astronomer, not a sailor or a trader. He showed Harry a trophy of those days. It was an astrolabe, a kind of map of the sky compressed down onto a sheet of brass, exquisitely made. It was descended from gadgets devised to show the faithful the correct direction for prayer.

Harry was intrigued to hear that in his youth, some decades ago, Abdul had served on the mysterious Chinese treasure ships that had once plied the Indian Ocean and beyond; Moorish and Arab navigators had always been prized by the Chinese.

Abdul had done well, and by the age of forty-five had been able to retire, 'to tend my garden', he said. But when open hostilities had broken out between the emir and the Christian monarchs he had come to the palace to work for the viziers. 'For this is a struggle for survival,' he told Harry.

Harry, listening patiently while sipping cold pomegranate juice, found it hard to believe that this elegant seafaring Muslim could be any sort of relation. And yet it was true.

Geoffrey Cotesford had discovered this branch of Harry's extended family, which for two centuries had been living in Granada. The first of them had been another Ibrahim. He had fled here from Seville when that city fell to the Christians. He had married a woman called Obona, adopting her child from a previous relationship. In Granada, Ibrahim and Obona lived to old age in peace, raising many children, and the family had prospered ever since. Abdul said the family still remembered Ibrahim. Abdul hoped his own patient service for his emir matched that offered by Ibrahim during the last days of Moorish Seville.

For Ibrahim and Obona, it turned out to be a good time to have come to Granada. The last great wave of Reconquest broke with the fall of Seville. In the natural shelter of the mountains, with support from the Islamic nations of the Maghrib, the wily emirs of Granada had been able to play off one Christian leader against another, and the terrible calamity of the Great Mortality had sapped the Christians' will to expand. Even the fall of the Baghdad caliphate to the Mongols had not harmed al-Andalus, which had gained a further measure of independence. It had been a period of uneasy truce – a peace that had lasted centuries.

But the truth was the emirs of Granada had always been vassals of the Christian kings. In return for security they paid heavy tributes in African gold, a steady bleeding.

And since the time of the Great Mortality, which the Moors called the Annihilation, Granada had slowly declined. It was all because of trade, Abdul told Harry. The strait to Africa had fallen into Christian hands, and Italian merchants monopolised the fruit trade, a vital component of Granada's economy, and drove prices down. But the Christian tribute still had to be paid, the defences maintained. Abdul said, 'I pay my taxes at three times the level of a Castilian. No wonder the emirs are unpopular!

'Still, the long truce endured. But it has all changed under our latest emir. The Christians call him Muley Hacen; his name is Abu al-Hasan Ali. He grew up seeing his father bowing before Christians, and he loathed it. About twenty years ago he refused to pay the tribute to Castile, and hasn't since. And three years ago Muley became aggressive, riding out to assault a fortified Christian town. It was a grave miscalculation. These new monarchs, Isabel and Fernando, are united and purposeful.

'And we Moors are suddenly disunited. There have been rebellions. Last year Muley was overthrown in favour of his son, Muhammad Abu Abd Allah, whom the Christians call Boabdil. But Muley's knights still support him. Others back Muley's brother Abu Abd Allah Muhammad az-Zaghall – El Zagal, the "Valiant One". And so it goes. There are rumours Boabdil is concluding secret deals with the Christians. Where once we played off one Christian nation against another, now the wily King Fernando plays us for fools.

'Last winter the long war proper resumed, after a pause for breath that lasted more than two hundred years, when the Christians assaulted a place called Loja. And I came to work in the palace.'

Harry shook his head. 'I can't understand such numbers. Two hundred years? How can a single purpose endure over such a huge time?'

Abdul laughed and topped up his drink. 'Men like you and I, Harry Wooler, traders and sailors, live in the moment, in the business of the world. But popes and caliphs, princes and emirs – those sort of folk like to believe they cast long shadows over history.'

Harry tried to get a sense of this cousin. He seemed intelligent, competent, and with a taste for beautiful things, judging by his clothes, and the wistful glances he cast out of the windows. But he was alone, without a family. Was he a man who preferred men? Whatever his taste he had evidently nothing but failed relationships behind him. And yet he had a place in this city, this ancient civilisation he obviously cherished.

He and Harry could hardly have been less alike, Harry thought. And yet here they were, related, considering working together.

He turned the conversation to the matter of the Testament.

Abdul said, 'I'll tell you the truth. In my family – or my branch of it – we have a sort of memory of prophecies. Of terrible weapons of war, of a man called the Dove, all of that. But if this was ever written down, it was long lost, and reduced to a memory of a memory. I don't think Ibrahim cared much for that sort of stuff. So why have you sought me out? Why come here, to al-Andalus? And why now?'

'It was Geoffrey's suggestion…' Harry had told Abdul of his contact with the monk. Now he produced a parchment on which the first twelve lines of the Testament of Eadgyth were written out.