‘They would still break down. Men would do better.’ He came to the thunder-mouth. ‘This is more promising. More compact than a catapult, perhaps. Faster to reload and reuse. But it does no more than a catapult would.’ He glanced around. ‘I see nothing here which would give one side an overwhelming advantage over the other.’

Peter sighed. ‘Well, you’re right about that.’

‘What we need,’ Subh said, ‘is Incendium Dei.’

‘Your mysterious Fire of God.’

‘Precisely. The fire that would turn these delicate gadgets into thunderbolts. ’

‘But you don’t have it,’ Ibrahim said.

‘Joan of the Outremer never replied to my letter. And I regret writing to her now, for I told her something of what we have, without learning anything of her. I fear she might become a rival, not an ally.’

‘Actually,’ Peter said, ‘it’s not just God’s Fire we need, Ibrahim. For these engines to be realised fully we need the original designs.’

‘Ah,’ Ibrahim said. ‘The Codex. The treasure said to be buried under the floor of the great mosque of Seville. Is that why you asked me here? To get me to dig up the mosque?’

‘No,’ Peter said. ‘I invited you here, frankly, because I thought you should be reconciled with your mother.’

‘But now that you are here,’ Subh said slyly, ‘why not? You have the ear of the vizier. If you dropped a word—’

Ibrahim shook his head. ‘You have buried yourself in this hole in the ground for too long. Think what the mood is like outside! In this crowded city the faithful wash around the muezzin tower like a sea. If I were to order the mosque floor to be dug up, in the hope of finding plans for super-weapons, I would cause a riot. And besides the imams would never give permission.’

‘So you turn your back on us again,’ Subh said, her tone poisonous.

‘I regret what has happened,’ he said. ‘Nothing should come between mother and son.’

Subh said, ‘But you still think I’m wasting my time down here, don’t you? You’re just as headstrong and unimaginative as you were as a boy.’

‘Yes. I still believe you’re wasting your time. And so, it seems, am I.’ He turned to leave.

‘If you won’t help us,’ his mother called after him, ‘at least don’t betray us. Don’t let the emir put a stop to our work. Trust me that much.’

He paused. Then, without looking back, he made for the tunnel that led to the air, and the light.

XX

XX

Saladin found London overwhelming, after three years away. When he arrived with Thomas early one morning, the city was blanketed by fog, thick, dense, yellow, stinking. People went around with candles in their hands and bits of moistened cloth held to their faces. Even by the river it was no better, and the ships crept cautiously along, lamps strapped to their prows.