Harry didn't want to hear this.

They lapsed into silence, as the countryside of England, echoing only to the bleating of the sheep, rolled past them.

V

York, within its rectangle of much-battered, much-repaired walls, was bustling, a city of trade. But it was dominated by its immense cathedral, the newest sections of which, only a few years old, were fresh-cut, bright and sharp. Geoffrey said the minster had been built on the site of a Roman military headquarters, and that the city after the Romans had become a sort of Viking trading capital, a tradition of commerce that still lingered. There were layers of history written in the stones, Geoffrey said, layers that shaped the present.

They stayed the night in the hall of Harry's merchants' guild. It was a grand building, with religious paintings hanging from the stone walls and long tables groaning with food and drink. Harry was made welcome. There was much business to discuss, for Harry only rarely travelled this way, and it was a great relief for him to be able to escape from Geoffrey and history and his family's complicated past, and to immerse himself in the real world of commodities and prices. Geoffrey excused himself and went to sit with the apprentices at the hall's service end. Later Harry found him in the basement, where the guild ran a small hospital for the poor, who were expected to pray for the souls of their benefactors.

In the morning they mounted their cart again and set off to find Harry's sister.

The church she had attached herself to, another Saint Agnes's, was a few miles north of the city walls. It was a small, modest establishment at the centre of a village built of stone recovered from a much larger, abandoned settlement, whose ruins lay all around. The church itself was quite new, in the Perpendicular style. But Harry saw it had been built on older foundations of blackened stone – perhaps a Saxon chapel burned down by the Normans; there had been a lot of that in this area.

They were greeted by the parish priest, a kindly, elderly man called Arthur. It was Arthur who had first called in Geoffrey to help him cope with Agnes's requests. 'But you must understand we very much value your sister's presence with us here,' he told Harry. 'Very much. She brings the love of God into our small lives…'

Geoffrey led Harry, not to the door of the church as he had expected, but to a side wall. Here a kind of cell protruded from the church's wall, with no door, and no window save for a slit.

And here, Geoffrey said, was his sister: bricked up in the cell within which she would spend her whole life. Harry stared in horror.

Geoffrey touched his shoulder. 'You must try to understand. This is the life your sister has chosen for herself. And she serves her people, you know. As the father said, most parishes are proud to have an anchoress attached to their church.'

A voice floated up from the slit window. 'Geoffrey Cotesford? Is that you?'

The tone was deeper than it had been, softer, but it was unmistakable. Harry's heart thumped; he had not realised how much he had missed his little sister.

'It is Geoffrey.'

'I knew you'd return.'

'Your faith in your brother was justified too.'

She gasped. 'Harry?'

Harry forced himself to speak. 'I'm here, Agnes.'

'Then come to my window.'

Harry knelt down. The window was a slit, just large enough to pass food and waste. Only a little light leaked into the cell within. He could see another window on the far wall where the anchoress was able to look into the church. The room was simply laid out, with a bed, a bench, a table, a crucifix on the wall. On the table were two books, a leather-bound Bible, and a copy of the Ancrene Wisse, the manual of the anchoress. The room's only other feature was a shallow trench in the floor. It puzzled Harry, who knew little of the lifestyle of an anchoress, a walled-in hermit.

And through the squint, this slit window, his sister's familiar blue eyes gazed out at him. 'I prayed you would come. I knew you would. You always did protect me, Harry.'

But, he thought, I did not protect you from this morbid fate. 'I have news of the family,' he said.

'My father is dead,' Agnes said softly. 'I know that much.'

'Mother is well. She misses you.'

'Tell her I pray for her…'

Geoffrey interjected gently, 'I will leave you to talk. But we must turn to business. Harry needs to understand why you summoned him, Agnes.'

'I would not have disturbed you,' she said. 'But I had to.'

'Why?'

'Because of what I found. In this cell…'

And she spoke of family legends: of Orm, who may or may not have sailed with the Conqueror, and Eadgyth, or Edith, the wife he may or may not have found demented and raving in the ruins of an old Saxon church outside York, while William's Norman thugs rampaged across the north of England.

'Do you know why I was called Agnes? It is part of the old story – my mother told me this – in every generation there is an Agnes, so we remember that Eadgyth's church was dedicated to that saint. And it is said that Eadgyth returned to the church later, when she sickened, and her mind failed. Poor Orm had to seek her here again.

'When I ran away from home, I was only ten years old. I had travelled no further than a day's walk from home. I had no idea what shape England was, Harry! The only place I had ever heard of that had anything to do with the family was Eadgyth's church near York. So I made my way here.'

'This is Eadgyth's church?'

'Rebuilt since then – but yes, it is her church.'

'Quite a journey for a child,' Geoffrey murmured.

'I hardened.'

Harry thought there was a whole desperate saga contained in those two words. He was full of guilt.

She whispered, 'I worked here, on the farms. I knew how to shear a sheep. Then I worked for the parish. And, in time, God and Father Arthur granted me the privilege of this, my enclosed life of prayer. My only stipulation was that my cell had to be here, in this corner of the church, on the old foundations.'

Harry guessed, 'Because this was where Eadgyth had hidden.'

'And where she came back to at the end of her life. I know this, Harry, because she scraped an account of her visions into the wall. The lettering is faded and lichen-choked, half-buried by rubble, old-fashioned and hard to decipher – but it is here. And as I dig my trench, I have uncovered it steadily.'

Harry felt a return of that uncomfortable dread, a sense of enclosure. He wanted nothing to do with this antique strangeness. 'I know the story of the man called the Dove,' he said. 'Who will be the spawn of the spider, and so on. And in the last days before the end of the world is due, he must have his head turned west to the Ocean Sea…'

Geoffrey quoted from memory, "'All this I have witnessed / I and my mothers. / Send the Dove west! O, send him west!"'

'There is more,' Agnes whispered. 'Orm remembered twelve lines. That is what we have come to know as Eadgyth's Testament. But there is more.'

'More lines scraped in the wall?'

'Yes,' Geoffrey said. 'Ten more lines, Harry. In which Eadgyth records her vision of what would become of the world if the Testament was not fulfilled – of a future in which the Dove turned, not west as he should, but east. I can see you're having trouble believing any of this, Harry. But when I tell you of this hideous future you will see why I summoned you here. Not just for your sister. We have to work out what to do about this. For we cannot let this dreadful future come about. He crossed himself.

Harry felt his whole life hingeing on this moment. He longed to flee from this madness, the woman in the hole, the terrible words scribbled on a wall, the memory of his dying, drunken father. But, as Geoffrey had seen, he had a sense of duty which would not allow him to walk away.