But in other ways Seville was quite unlike London. He walked to the site of a grand cathedral, bristling with scaffolding. It would be the largest in the world, it was said. But it had been built on the site of the city's Moorish mosque, and a surviving muezzin tower still loomed over it; slim and exquisite, the tower would always draw the eye away from the solid pile of the Christian church.

And just over the plaza from the cathedral was an old Moorish fortress-palace which the Moors called the al-qasr al-Mubarak, and the Christians called the Alcazar. James peered curiously through its arched doorways. Though the Moors had been expelled from Seville by the city's conquerors, later generations of Christian rulers had brought back craftsmen from Granada to work on these buildings, maintaining and even enhancing them.

Seville was not like London, then, where with their forts and cathedrals the conquering Normans had erased any symbol of the old Saxon state. Here the spirit of the Moors lived on in a Christian country.

Perhaps things were going to change, however. Two hundred and thirty years after its conquest Seville was still the southernmost Christian city in Spain. The great tide of Reconquest had stalled. The Christians were distracted by conflicts between their own rival kingdoms, and their vast project to repopulate the occupied country was diluted by the Mortality; where once the Moors had turned the land green, now only Christian sheep grazed. Seville remained a city on the cusp of a great change, James thought. Perhaps it was no wonder that apocalyptic legends had gathered around the place.

But James, in his first walk around this strange, complicated, muddled city, did not see a need for cleansing, but a kind of mixed-up human vitality he rather relished.

Near the Alcazar he came across two girls who sat on a bench, eating oranges they unpeeled with their thumbs. No older than twelve or thirteen, dark, shy-looking, they giggled with each other as they ate, but kept a wary eye on the folk around them. The girls both had yellow crosses stitched to their blouses. They were Jews, then. They had to wear ugly symbols on their clothing, but at least they were here. In England there were no Jewish girls like this, laughing in the sun and eating oranges.

When the girls saw James watching them, they looked away nervously. Embarrassed, annoyed at himself for frightening them, he hurried on.

He made his way back to the river, and walked to a complicated pontoon bridge of seventeen barges.

And across that bridge he glimpsed the brooding pile of the castle of Triana. It was the headquarters of the Inquisition.

Before travelling to York, Harry returned to Oxford for a few days to put his affairs in order.

Then he joined Geoffrey Cotesford on the great north road, the old Roman route that ran from London to Scotland. Harry would have preferred to make his way by sea, which would have been far more comfortable, but Geoffrey pleaded poverty. So they clattered away in their cart, Harry wincing as they hit every pothole. In places the way was difficult because of fences left untended, bridges unrepaired, work left unfinished for more than a century because there was nobody to do it.

Geoffrey pointed out features of the landscape. 'Still empty – I told you!'

Here was a town half given over to farmland. Here were villages abandoned altogether, the roofless houses slumped like old men, the fields overgrown. Swathes of the country had been given over to herds of sheep, which bleated piously as they nibbled the grass that grew around the ruins. Harry usually rode past such grassy mounds of tumbled walls and abandoned buildings without looking too closely; they were just part of the landscape. But Geoffrey was pitiless.

'The country has a way of cleansing itself. Crows and rats and flies! Even they have a purpose in God's grand scheme. But we have never come back, Harry; we have never taken back our villages.'

'Why are we talking about the Big Death again?'

'Because it shaped your family, Harry – or, rather, reshaped it. This is what I have discovered about you. The empty world after the Mortality was quite different from what went before. Suddenly there were too few folk to get the work done; a bad lord could not hold onto a man, for there was always work somewhere else. There were revolts as the nobles tried to stuff everything back into Pandora's box, but it was too late. And opportunities opened up.'

'Such as for my family.'

'Yes! Your grandfathers saw the chance to slip the bonds of allegiance to the lords. You became merchants, wealthy in your own right, and you called yourselves Wooler – you had no surname I can trace before.'

'And before the Mortality? What were we then?'

'You were soldiers – perhaps all the way back to the days of William. It's said you had an ancestor who came over with the Conqueror. But then every family in England says that. Certainly your forefathers fought alongside Edward Longshanks.'

'The Hammer of the Scots.'This story of a lost and different age rather thrilled Harry the merchant.

'And before that they rode with him to the Holy Land, for Edward was a great crusader. But to your family the crusades weren't a mere adventure. To them, the Holy Land was home – or had been.'

And he told Harry of his ancestor Saladin, born and raised in the Holy Land, who had come to England, and fought in Spain, and then joined a crusade. Surviving, he returned to England to start a family of his own. 'Saladin was always determined that his family should remember the Testament of Eadgyth; he thought it contained important lessons for the future. Your own father taught it to you, didn't he? But other prophecies accreted around you too…'

The news about Saladin was disturbing for Harry. 'Then I might have Saracen blood in my veins.'

'A dash of it, probably,' Geoffrey said. 'Don't worry, I'm keeping this to myself. I wouldn't wish to harm your business reputation. Be grateful there's no sign of Jewry in your blood line. But then, Edward Longshanks expelled all the Jews from England nearly two hundred years ago, by God. We were the first in Europe to do it, and we set a fashion, didn't we?'

Harry, impatient, asked, 'Just tell me simply – why are you so interested in my family's past?'

'Because you will need to understand your own complicated history if you're to understand what has become of your sister. Poor Agnes! I got involved, you know, because my house is not far from the parish church where she lives.'

'She lives in a church?'

'You'll see. I was brought to her. But she was calling for you, the brother she hasn't seen for ten years. You always protected her, she said.'

'So I did, I suppose,' Harry said uneasily. 'My father was always short with her. And when he was in his cups – I deflected his blows a few times. He repented before he died; I forgave him.' Harry didn't enjoy talking of his family's past; it hadn't been a happy time. 'But my sister disappeared – she ran away, she was no older than ten. We heard nothing more of her.'

'You didn't try to look for her?'

'At first. But after my father died I took over the business, and found he'd run it down – squandered the legacy of my grandfather. It was hard work restoring it. I had no time.'

'I understand. And in all probability your sister didn't want to be found. But she did not die, Harry; somehow she survived. And she found a place in the world. But eventually her troubles overwhelmed her, and she asked for you. So I came to find you.'

'It's good of you to do this,' Harry said, though he felt resentful rather than grateful. 'To come all this way, to give up your own business for her.'

'You're welcome. But it isn't just charity that motivates me. I rather think your sister's plight has a wider significance.' He eyed Harry. 'I know you're a sceptic, Harry, about matters beyond the material, and that's healthy. But the fact is your family is steeped in prophecy…'