Joan said, ‘If the Codex exists at all, it is lost under this ocean of flooring.’

‘Not lost,’ said Subh. ‘I know where it is. Precisely.’ And she told them of a memoir left by Ibn Hafsun, the muwallad who, more than a century ago, had been the man actually to bury the Codex at this site. ‘I had a scholar, Peter, who analysed his record and calculated precisely where under the mosque the cache must be. I had hoped we could work together,’ she said. ‘That is why I wrote to you. In trust. With the two scraps of knowledge that have come down to us, the engine designs and the enigma of the Incendium Dei—’

‘Tell me where the Codex is.’

‘Not until we discuss terms.’

Joan laughed in her face. She turned to Michael. ‘Hold her.’

Michael drew his sword. He stepped forward and took Subh’s arm. Thomas flinched, upset by the bit of violence.

Subh’s face was coldly furious. ‘I came here for a civil negotiation.’

Joan said, ‘I will not bargain with a defeated Moor.’

‘You will not find the designs without me.’

‘Oh, I will. Perhaps not today. Perhaps not for a year. But with time, there will be a way. Do you doubt that? The only question is, will you cooperate? For, you see, the only chance you have to gain anything from this situation is if you tell me what I wish to know.’

Saladin put a hand on her arm. ‘Mother—’

But Joan shook him off.

Subh was beaten, but she was unafraid. ‘Very well.’ She glared at Michael until he let her go. Then she turned and pointed to the bonfire blazing in the middle of the mosque. ‘There. About six paces beyond that bit of arson by your brutish soldiers.’

‘Good,’ said Joan. ‘Let’s get on with it.’

Subh stood before her. ‘And what of the bargain you made with me?’

‘What of it? You are Muslim, I am Christian. All over the world, we are at war. And the engine designs are the spoils of war. I told you whatever was necessary to take those spoils.’

Subh stared back at her. ‘So you betray me.’ She wasn’t begging, Saladin saw with grudging admiration. Unarmed, alone, surrounded, she was thinking, trying to find a way into Joan’s soul. ‘Cousin. We have different faiths. But we are family, you and I - and Saladin. I have a son too, called Ibrahim.’

‘I am not like you,’ Joan said coldly.

Subh insisted, ‘We are the same blood. With roots in this very country, where once a foolish boy called Robert met a girl called Moraima. Is that not a deeper unity than anything else, even than differences in faith? Must it go on and on, Joan, Christian against Muslim, century after century as it has already for half a millennium in Spain, until none of us are left alive?’ And she reached out a hand.