Saladin and Thomas were not permitted to go with the scouting party to the foot of the walls beneath the strange explosion. But they were able to inspect what was recovered: some twisted bits of metal, and an immense ball of iron.

'An engine,' Thomas said darkly. 'Or the remains of one that failed.'

'Subh,' Saladin said. 'My mother's cousin. She is in there. This proves it.' He glanced at the city walls, and wondered if this remote relative whom he had never met was looking back at him now. 'She must have the engine plans. She must have dug them up from the mosque-'

'Not necessarily. Fernando has the city riddled with his spies. If that were going on we'd have heard about it. Subh's letter to your mother hinted of other designs, sketches developed by Sihtric and his co-workers from the originals – sketches that were not entirely lost when Sihtric died. Perhaps that's what we're seeing here.' He grunted, poking tentatively at a bit of torn copper sheet. 'It would certainly explain why it failed. We may yet not be too late to get to those originals first.'

'I hope so. Or mother will be furious.'

Word came from the vizier's office that King Fernando was prepared to accept the surrender of the city on the twenty-third of November. Three days before that cut-off the emir's ministers were to meet with representatives of the King and the Pope, where Fernando's terms would be presented.

Ibrahim was dulled by the months of siege. But Ibn Shaprut counselled him to be hopeful. Perhaps in this moment of surrender the Christians might discover in themselves the mercy of Jesus of which they boasted so loudly.

On the morning of the meeting, Ibrahim woke from a restless night, soon after dawn. He could hear rain hissing down.

Ibrahim left the palace and walked the streets of the city, hoping to clear his head. The rain on his upturned face was light and fresh. The people were coming out of their houses, men and women with scrawny arms protruding from grimy sleeves. They put out pots and bowls and cups to catch the rain. This was the first significant rainfall of the winter, and Ibrahim imagined it cleaning the air, washing away the last of the heat and stench of the filthy summer of siege. The world was being kind to Seville, then, at last.

But it had come too late. The bodies bundled into doorways or heaped in alleyways told him that: the night's dead, dumped by those too weak or apathetic to dispose of them properly. Ibrahim made a mental note of where the corpses lay, so he could brief the day's working parties. But he supposed that in a few more days such problems would be the concern of some Christian soldier, and he, at last, could rest.

He walked down to the river, where no ships sailed this morning, and the waterwheels stood idle. It struck him how very quiet the city was now. There were few animals around; in a starving city the dogs and cats had gone into the pot before the rats. Even the songbirds had been netted, plucked and consumed. Few children too, and fewer old people. Ibn Shaprut the doctor had told him how hunger and disease and drought always took away the very old and the very young, always the most vulnerable.

He tired quickly as he walked, and his burned back still ached sometimes, and the cold of the rain cut into his flesh. After months of rationing there were times he felt so light and flimsy, so detached from reality, that it was as if he had become a ghost, haunting the streets of the city he had tried to help save.

He had wandered far enough. He turned back.

Inside the emir's palace Christian troopers gawped at the tiles and the frescoes, and leered at the Muslim women. The Christians wore chain-mail and steel helmets, and had bright red crosses emblazoned on their shoulders. These were crucesignati, crusaders, holy warriors, infused by piety and blessed by the Pope. But they were nearly as ragged and half-starved as the surviving population of the city itself.

Ibrahim walked across the patio outside the turayya, the hall at the centre of the suite of rooms called the Pleiades, and the grandest in the palace complex. The patio was a lovely rectangular space encompassed by a gallery of delicate trefoil arches. One Christian soldier had taken his boots off and was soothing his filthy, blistered feet in the rainwater trapped in the fish pond. His mate saw Ibrahim pass by and kicked the bather, speaking in rough Latin.

'Get up, Michael, you arse, you're showing us up.'

'Oh, leave me be, Saladin. Arse yourself. This isn't so bad, is it? Not so bad for soldiering…'

Ibrahim was surprised by that famous Saracen name, Saladin, given to a Christian soldier. But Fernando's army was international, drawn from all across Christendom. 'Saladin' could have come from anywhere.

He walked on into the turayya itself, where he found that the discussions had already started. The Christian party had lined up against one wall, and glared at the emir's representatives, led by the vizier, who clustered opposite. Hapless servants, trembling with fear, scurried between the parties with trays of sweetmeats and wine. The Christian leaders were warriors and clerics, knights and princes, envoys of the Pope. Some were both military and pious; Ibrahim saw a man in a tonsure with a chain-mail vest over his monk's habit. And they all wore the shoulder-cross of crusade.

There was only one woman in the Christian party. She was still young, in her thirties perhaps, and quite pretty, with a face like an almond. A fat elderly monk accompanied her. Pretty or not she glared at her Muslim opponents as severely as any of the men.

As for the Moorish party, Ibrahim spotted Ibn Shaprut at its heart – and, he was shocked to see, his own mother stood close by.

He walked up. 'Mother. What are you doing here? It's hardly safe.'

Dressed in a robe as white and clean as mountain snow, her face shining with expensive oils and her hair drawn back under her veil, Subh looked magnificent. Magnificent, but furious. 'Safe? Where is safe? None of us is safe, Ibrahim. Well, none of us save for him.' She pointed.

Ibrahim glanced across the room. There was the almond-faced woman, and beside her, talking animatedly to her and her monk companion, was a flabby, sleek, sweating Moor.

'Ali Gurdu,' Ibrahim said with disgust. 'That grafter. I should have cut off his hands and feet while I had the chance.'

'What's done is done,' Ibn Shaprut said. 'You can't blame him for trying to save himself. And he might even help, though he doesn't mean to, if he makes the Christian passage into the city a little easier.'

'"Makes the Christian passage easier",' Subh snapped. 'What are you talking about, you quack? Do you understand nothing of what's happening?'

Ibrahim frowned. 'What do you mean? Fernando has the city. What else can he want?'

'Expulsion,' said Subh.

'What?'

'We must leave. Every Moor – all of us who can walk, and even if we can't. That is the condition Fernando is going to impose. Fernando doesn't want a living city. He doesn't want us. He only wants the stones, to house a new population of Christians.'

Ibrahim was stunned. The room spun around him, and the rich colours faded to yellow-grey. He felt Ibn Shaprut's strong hands on his shoulders, and he was helped down, to sit on a heap of floor cushions.

Ibn Shaprut offered him a cup of watered wine. 'Drink this.'

Subh stood over him, glaring, a pitiless mother. 'You've worn yourself out, and for nothing. I told you so, but would you listen to me? Now look at you – fainting like an old woman, in this hour of our family's greatest crisis.'

'The family.' His own voice sounded distant to Ibrahim. 'What does the family matter? It hasn't been like this before. Even in Cordoba. There Muslims still live under Christian rule, as once Christians lived under our rule.'