'So it all went wrong. Then what?'

'Ibn Tufayl tried to destroy the machines Sihtric had made, and to eliminate the scholars who had worked with him. He wanted it all for himself. He dreamed of being more than a vizier, lady.'

Subh nodded, matter-of-fact. 'He wouldn't have been the first. I take it he didn't achieve his ambition?'

'No. As they fought he burned himself to death, along with Sihtric and Orm, and the plans for the machines. All this took place in the palace of Madinat az-Zahra.'

Subh looked at him shrewdly. 'Not all the plans were lost. Or you would not be telling me about this now.'

'You're perceptive,' he said. 'No, not all of them. Ibn Tufayl doesn't seem to have been very competent. There are hints of personal weaknesses in the records – I suppose that doesn't matter. He was certainly not efficient in his elimination of Sihtric's work. I was able to find traces in the archives. For instance, one young clerk survived the vizier's cull, and, in bitterness, wrote down all he remembered to thwart the vizier's purpose. There are similar relics. It's all very fragmentary – most of it is just the point of view of one junior clerk – but-'

'You have these fragments?'

'Some of them. And, more than this – the blaze did not destroy everything. Moraima and Robert escaped. Between them they took away the Codex of the Engines of God – the original designs brought by Sihtric to Spain.'

'And what did they do with them?'

'The two of them fell out. They could not agree. The plans were buried – but what was buried was fire-damaged and not complete. One comer had been torn away by Robert, perhaps intentionally, perhaps not. This fragment contained the secret of God's Fire. Possibly – it is said. And it may be that Robert took away another treasure, another prophecy entirely, called the "Testament of al-Hafredi". I know little about that. But as for the rest of the engine designs, a man called Ibn Hafsun buried them for Moraima.' He thought it over. 'I suppose he may have been an ancestor of your Alonso the Fat.'

'How ironic that would be,' Subh said drily. 'And where did he bury the plans?'

Peter hesitated. 'Under the floor of the great mosque in Seville. In fact I have seen a fragment of memoir by Ibn Hafsun, in which he specifies exactly where the Codex can be found.'

Subh laughed. 'Now you're being absurd. Peter of Toledo, you must know that in a country where war has washed back and forth ever since Tariq crossed the strait, there are legends of buried treasure under every rock.'

'But it may be worth looking,' Peter said softly.

'You have an adventurous soul, for a scholar. And these sketches, the fragmentary plans you say you already have-'

'I'm no engineer. But I believe they could be developed into workable designs.' He said this with pride, and a certain longing, for it was a project he would find fascinating to pursue if he got the chance.

She clapped her hands, almost girlish. 'Oh, how marvellous. But you're telling me that even if I could get to Seville, even if we manage to dig up the mosque and find these plans – even if! – they will remain incomplete.'

'Because of the fragment taken by Robert, yes. But I have some news about that too. I was able to trace this Robert, son of Orm, and the family who followed him.'

She studied him. 'You are resourceful, aren't you? How?'

'It wasn't hard. He became known as Robert the Wolf.'

She sat back. 'Ah. One of the most notorious of the crusaders.'

'He settled in the Kingdom of Jerusalem, which he helped to found. His family live there still. Perhaps they know something of this Fire of God.'

'What do you suggest, Peter of Toledo?'

He shrugged. 'Write to the head of the family in the Outremer. She is called Joan. Tell how you may be able to help each other. I have a contact in a monastery in Colchester who could put us in touch.'

She scoffed. 'A mudejar of Cordoba writing to a Christian family in the Outremer? You really are a dreamer, aren't you, Peter?'

'Why not? You have two pieces of a puzzle, it seems to me, you and this Joan of the Outremer. And if you put them together it might be mutually beneficial.'

'And you, Christian Peter, would put these marvellous weapons in the hands of a Muslim? Would you have us make these weapons and slaughter each other?'

'The weapons may make war too dangerous to wage. Or the engines could be turned on the common enemy.'

'The Mongols,' Subh said. 'Now there's a thought. Well, don't worry, little Archimedes. I do sense an opportunity in these engines. But I'm no al-Mansur; business is what I know. All I want is to protect my family and my own. But if I can make a little money out of this I'll do it.' She smiled at him. 'You've done far more than I asked of you, Peter of Toledo. You've earned your fee.' But he kept his face serious, and, watching him, she grew grave. 'Ah. But you said you had something I would not wish to hear.'

'I do.' And, having witnessed a near-stoning that day, Peter knew how painful it was for her to learn that her ancestress Moraima was not just the daughter of a Christian, Sihtric, but the consort of another, Robert.

Subh was devastated. 'By Allah. But that means that Moraima's child, my distant grandfather, was three-quarters Christian. And by a brute of a crusader like Robert! No, no, it couldn't be worse. And to think I mocked that fool Alonso for the impurity of his blood!'

Peter said, 'All this was generations ago.'

She got up and paced, her movements hard, full of anger. 'You don't understand what it's like here, where Christianity rubs up against Islam. We are polarised. I have pinned my entire identity on my descent from the vizier. Nobody has heard of Sihtric, nobody cared about him. But if the vizier's granddaughter bore the bastard child of a notorious crusader, I am ruined in this city.'

'No one need know,' Peter said helplessly.

She laughed at him. 'Alonso will learn. He can afford better scholars than you, Peter. So that's that. I must flee Cordoba after all – and we may get a chance to explore Seville sooner than you expected.' She glanced at the angle of the sun. 'I have much to do. Scholar, find yourself a servant. Any of them will do. Have a room made up. We should still write to this Joan of the Outremer. Draft something for me, will you? Now you must excuse me. Ashmet? Ashmet!'

She stalked indoors, leaving Peter on the patio with the orange drink, and the dried fruit, and his pack with his notes.

It was a deep shock to Saladin of Jerusalem to learn, from what Brother Thomas related of Peter's letter to Colchester, that Robert the Wolf, hero of the First Crusade, his family's saintly forebear, should be tainted by a liaison with Moraima, a Moorish girl.

'Now maybe you see what he had to run away from,' Joan said. 'All the way to the Holy Land-'

'Don't talk like that. Robert took the Cross. He didn't run anywhere.' Saladin got up, dusted off his leggings, and walked down the hill to the horses.

'I knew you'd react like this. You really are such a pious prig! But you don't need to worry,' his mother said, as she got up more stiffly. 'He tupped this girl, then left her in al-Andalus. He married your distant ancestress later, and she was a respectable Christian; there can be no blood of Muslim ancestry in you.' And she added, so softly he wasn't sure if she had spoken at all, 'Not from Moraima, anyway… Come. We must prepare for the arrival of Brother Thomas.'