The light was extraordinary in this holy country, thick and dense, crushing. It seemed to oppress the old city with its broken walls and shining domes, rather than illuminate it. Thomas, utterly exhausted, felt close to collapse. But here he was before Jerusalem itself, standing in the footprints of Christ. Overwhelmed, he brushed the dirt from his robes and scraped the sweat from his brow, and dropped to his knees to pray.

He was aware of Joan and Saladin, swathed in their white Saracen-like robes, watching him with some bemusement.

Joan led him into the heart of the city, with a serving boy who spoke not a word of English or Latin following behind with Thomas's pack. Thomas was soon lost in the maze of jumbled streets. There was a feeling of crush, of shabbiness, and Thomas saw that some of the buildings had been assembled from broken and ancient stones. Age lay heavy here.

To get to Joan's home he was led through a narrow alley to an inner court around which tall houses clustered. Joan entertained him in a large open room, with a thick carpet and heavy hangings on the wall. The windows, just slits, were so small that oil lamps burned despite the intensity of the light outside. It was a room that might have graced an English manor, he thought. But this was not England, where you strove to keep in the warm; the room was hot and stuffy, thick with smoke, arid sweat started from his brow. It was an inappropriate, stubborn architecture.

Joan served him watered wine. 'You are an unaccustomed traveller, brother,' she said.

'I'm afraid so. I prefer to journey in the imagination, in the pages of my books, rather than to haul this weary carcass across land and sea.'

'And yet you have come as far as Baldwin, and those who first took the Cross.'

'The crusaders arrived fit to fight. They came to build kingdoms! I scarcely have the energy to make up a bed.'

'Oh, that is done for you,'Joan said. 'And while we don't expect you to conquer the city for us, you must see it. I want Saladin to show you around. No, I insist.'

Saladin nodded, looking surly, reluctant.

Joan's English was stilted, her accent a kind he had never heard the like of before. She was a slim woman, with a pretty, oval face and a pale, very English complexion – unlike her son, who was so dark he was all but invisible in the gloom of this absurd hall. The mother looked out of place here, a northern flower that ought to wilt in the sultry fire of the sun. Yet she was prospering, even though she had lost her husband and father before she was twenty.

This was a complicated place, he reminded himself, the Christian culture of the Outremer an exotic transplantation that had survived in this alien soil for nearly a century and a half. He must keep his wits about him.

'It is good to meet you, at last,' he said. 'I corresponded with your husband, and indeed your father before he passed your affairs on to your husband.'

Joan smiled at her son. 'Thus Brother Thomas has served our family's interests for generations.'

'You make me feel old,' Thomas said. 'But conversely your family's generous bequests have sustained the good work of my house for just as long.'

'Then we both benefit.'

The boy did not seem very interested. 'My mother said you have come to deliver a letter.'

'Among other things.' Thomas reached into his robe, and extracted a wallet of pigskin. He handed this wallet to Joan. 'It is from your cousin in Cordoba, as I indicated. Subh, a matron of that city.'

She drew out a bit of parchment, neatly folded but with a broken seal. She read a single underlined phrase. 'Incendium Dei. I wonder what she means by that.' She held the letter before her small nose. 'I would like to imagine I can smell the oranges of Spain in the ink. Robert the Wolf would say little of his time in Spain, but he spoke of the orange trees. It's the sort of detail that survives in the telling.'

Thomas smiled. 'It probably smells more of the sea by now, madam. I have one other piece of news for you. The Mongols.'

'Their advance into Europe continues, does it?' Joan asked.

Thomas shook his head. 'They turned back at the gates of Vienna.'

'No!'

'It happened just this summer. It was on the death of the great Khan Ogodai. The Mongol generals immediately returned to their capital, for it is their custom to gather there to debate the succession.'

'Well, that's not in old al-Hafredi's foretelling.'

'Truthfully the document is unclear, madam. I may know more later in the year; I intend to meet with the Pope's legate, who was at the Mongol court when the reverse came. We must discuss the implications of this.'

'Of course.'

Saladin looked from one to the other. 'You realise I have no idea what you're talking about. Moorish cousins in Cordoba? The Mongols at Vienna? What does any of this have to do with us, here in Jerusalem?'

'It's a tangled story,' Joan said. 'It all stems from Robert and his strange adventures. You'll learn it all, Saladin.'

'I'd rather not,' the boy said briskly.

Thomas had come across warrior cubs like this before, who put sword-swinging ahead of scholarship. He saw it as part of God's purpose for him to correct such attitudes; he did not believe God wanted ignorant soldiers. And in this case it was essential that Saladin understood. 'It is your duty to hear.'

'Really.' Saladin got up abruptly. 'I've got things to do. Find me when you'd like your tour of the walls, Brother Thomas. Mother.' He nodded to Joan, and walked out.

'I would apologise,' Joan sighed. 'But he's always like this.'

'I sense he has a good heart.'

'And a strong soul,' she said. 'He'll do what's right.' She glanced again at her letter from Cordoba. 'Although I pray we will all find the way to do that.'

Heading south-west along the bank of the Guadalquivir, Subh's caravan slowly moved out of the hinterland of Cordoba, with its sprawling farms and market gardens and groves of orange trees. The country broadened to an immense plain, the horizon obscured by a ghostly heat shimmer. It was an arid, open, severe land, littered with ruined forts like the hulks of wrecked ships.

Peter imagined it must be easy enough to get lost out here, on a land as vast and flat and featureless as an ocean. But not long after leaving the city they passed another mule train going the other way. The muleteers greeted each other noisily. In this sea of sand the muleteers were the navigators and the captains, stitching together the country with their endless journeying. And the muleteers sang, wailing muezzin-like melodies with earthy words in a rough Arabic. The songs were not so much long as open-ended, as one driver after another added a verse to an already complicated saga. So compelling were the choruses, so simple the melodies, that it was impossible not to join in, and the steady rhythm of the songs chimed with the pounding of the mules' hooves.

Peter, fanciful, found himself admiring the stoical simplicity of such a life. He envied the muleteers their sinewy strength, their obvious comfort on the rolling backs of their mules. To be bound into such a monkish routine, to learn to be able to do at least one thing exceptionally well, would itself be a kind of devotion. But he knew he could not bear such an elemental existence, not when there were cities full of books waiting to be read, a universe of philosophies to be contemplated.

And he was not so naive as to idealise the muleteers' life. They were all heavily armed, with knives, swords and cudgels, and none of the caravans was small enough to be vulnerable to attack by the pirates of this desert sea. The shifting frontier line between Christendom and Islam made this a dangerous country to travel, and it was well known that refugees from the lost Moorish cities, always streaming south, were easy targets for killers, rapists and thieves. Subh had taken care to plan against such a calamity for her party.