The caravan was allowed to enter Seville without incident.

The city was more of a sprawl than Cordoba, and had long eclipsed its illustrious rival, becoming the capital of the Almohad rulers of al-Andalus. And, though Cordoba had fallen, this remained a Muslim city, not a Christian one; the crescent flew high over the domes and minarets, not the cross, and there was nothing plaintive about the muezzins' calls to prayer.

But there was evidence of the Christian Reconquest even here. Where Cordoba had seemed depopulated Seville struck Peter as very crowded. The towns and cities of the south had had to absorb the floods of refugees from the grinding advance of the Christian armies, and Subh said that she believed the population of the city might have doubled since the fall of Cordoba.

And it was a city under threat. Seville had the natural advantage that the Guadalquivir was navigable from the sea as far as this point, but that brought a certain vulnerability. So, near the heart of the city, two squat towers faced each other across the river. A massive chain stretched between them, that could be winched up to span the river to block the passage of threatening ships. Peter was taken by the brutal simplicity of the device.

As they threaded through the city Peter glimpsed the courtyard of the great mosque, crowded with fakirs and imams, and with the faithful who performed their ritual ablutions in the many fountains. It scarcely seemed conceivable that beneath the feet of those swarming faithful could be ancient plans for deadly weapons, plans lost and buried for more than a century, while this shining mosque had mushroomed over them.

Despite the overcrowding Subh had been able to secure a house, smaller than the one she had had to abandon in Cordoba but with a decent patio and fair-sized rooms, and not far from the great mosque. Here, once she had paid off her muleteers, she lodged herself, with Ibrahim and a few of her many family members.

And she gave a room to Peter. He peeled off his travel clothes with relief. He imagined he had sweated away half his body's weight into the fur of his wretched, patient mule. That night, in an airy room and on a soft pallet, out of the iron stink of the desert, he slept more deeply than he had since he was a child.

Joan's smoky English hall was scarcely less tolerable in the evening's cool than in the heat of the day.

And here Saladin was told the strange truth about his family.

'It's a tangled story,' Thomas said, studying Saladin, trying to gauge what he understood. 'A story of prophecies – not one, but three of them, a whole sheaf.'

Joan told Saladin, sketching in brisk, efficient strokes, the story of how over a hundred and fifty years ago Robert the Wolf had travelled to Moorish Spain with his father, Orm the Viking, in search of a rogue priest.

Thomas said, 'Sihtric had come into the possession of plans for marvellous weapons. These plans were called the Codex of Aethelmaer, the weapons the Engines of God. But the Codex was compressed and enigmatic, and contained words nobody could read. So Sihtric went to Moorish Spain-'

'What? Why?' Saladin sounded outraged. 'To hand these weapons over to the caliphs?'

'The caliphs had gone by then,' Thomas said patiently. 'But, no, it was not Sihtric's intention to give his weapons to the Moors. He hoped to use the Moors' greater scholarship to help him understand the Codex and develop the weapons. And then, so his scheme seems to have gone, he would turn the weapons on his Moorish hosts.

'While he worked on these plans, as he researched the past, he came upon the second of the three prophecies – a sort of sketch of the future left by a wizard called al-Hafredi. More of that later.

'And then Robert and his father, Orm, turned up. Now Orm had a vision of his own – the third prophecy. He called it the Testament of Eadgyth.' And he repeated Eadgyth's legend of the Dove, who must be turned to the west.

'Lots of prophecies, then,' Saladin said, confused.

'Orm believed his Testament of Eadgyth warned against the use of the Engines of God. That is why, armed with the Testament, a troubled Orm travelled with his son to the distant land where Sihtric was developing his weapons.'

'And in the middle of all this,' Joan said drily, 'our ancestor Robert found time to fall in love, and implant his seed in the loins of a Moorish girl, Moraima.'

Saladin was intrigued despite himself. 'So what happened to them all?'

'It all went predictably wrong,' Thomas said, and he sighed over the foolishness of the long dead. 'There was a fire. The result of some struggle, probably. Orm and Sihtric were both killed. The prophecies and plans were lost, or so it was believed…'

Robert came home, seemingly full of disgust at what he had experienced of Moorish Spain. He became a warrior of God, eagerly taking the Cross when the Pope called the First Crusade.

Thomas said, 'But he never forgot his strange experiences, the tale of the magical engines, his father's prophecy, the future visions of al-Hafredi. In the end, driven by some sense of guilt perhaps – he may have felt it a betrayal of his father to just abandon it all – he told his own eldest son the whole story. And that son, mercifully for history and your family's fortune, was more bookish than his father, and wrote it all down for us.

'Now, by chance, not all of the Codex itself was lost. In the final struggle a scrap of it was torn away and ended up in Robert's possession. It bore strange words…' Thomas rummaged through scrolls on a low table before him for his copy of the fragment. 'Ah, here we are.' He ran his finger along a line of text.

'There were letters nearby too, preserved on the fragment, but ripped through. AD, perhaps, a V and an M – nothing else could be made out.'

Saladin read this over. 'It's in no language I ever saw.'

'Reading isn't your strong suit anyhow, son,' Joan said, mocking him.

'This is no known language,' Thomas confirmed. 'I believe this is a cipher – a code, perhaps of the type Caesar once used. There may be some key, which is lost. At any rate it was preserved, thanks to the transcription of the bookish son.'

'Now,' said Joan. 'Here's the most important thing for us, Saladin. Another of the three prophecies, the Testament of al-Hafredi, also fell by chance into Robert's hands.'

'Written on a bit of human skin,' Thomas said with a certain morbid relish.

'And this al-Hafredi has become our family's own oracle.'

'An oracle?'

'I mean that literally, Saladin. One of Robert's grandsons gave the material to Brother Thomas's house to study and interpret it for us, and so they have, in the centuries since.'

Thomas said, 'Al-Hafredi told of events to come – very broad-brush, but reliable none the less. And in particular he spoke of the advance of the Mongols. This followed the Islamic conquest of Europe, and he described it step by step.'

Saladin was trying to work this out, his face twisting. 'The Muslims have never conquered Europe.'

'True, but we can believe that the Mongols' advance would have occurred as al-Hafredi described it, whether Islam conquered or not.'

Now Saladin seemed utterly baffled. 'And Robert lived and died long before anybody had heard of the Mongols!'

'He did indeed,' Joan said. 'It wouldn't be much of a prophecy if it was the other way around, would it?'

'But how can this be? Who but God can know the future?'

'Ah,' said Thomas. 'An interesting question.'

'Which,' Joan said hastily, 'we can explore at our leisure another time. For now, Saladin, the important point is that this information has proved useful.'