The vizier nodded. ‘Your Codex is here, the sketches you stole from Aethelmaer.’ He held up a scroll. ‘So are all your notes and commentaries, and the designs you have developed. All your work is here.’ Ibn Tufayl smiled, malicious. ‘And if I ordered it destroyed, perhaps on a mere whim, it would be gone for ever. The meaning of your life, priest, gone in a heartbeat.’

‘You would not,’ shouted Sihtric, his face reddening.

Orm said, ‘Oh, calm down, priest. He’s only goading you. It’s obvious he won’t destroy your work. It’s far too precious to him for that.’

The vizier nodded. ‘I’m glad one of you shows some wisdom.’

‘But you have your own purpose for them, no doubt,’ Robert said.

Ibn Tufayl half rose. ‘Do not speak to me, you wolfling, or I will have you eviscerated before your father’s eyes.’

Robert was shocked by the anger in his face, the crimson glower, the twisted lip, the bulging eyes. He flinched, unable to understand why he should be the focus of such rage.

Orm’s grip tightened on his arm, hard enough to hurt. ‘Stay calm.’

Sihtric said, ‘He’s right, though, isn’t he, vizier? You have concocted your own scheme for the weapons.’

The vizier settled back. ‘Oh, yes. Far beyond your petty notions. It takes a man of vision to see the true path. But oddly, it was you who put the vision into my head, priest. You and your muscled friend here. All your talk of al-Hafredi of Poitiers, this bizarre fantasy of men flung across time, a history averted. Nonsense! Irrelevant! No wonder you Christians fail if your heads are addled with such maundering. And yet the scheme you unfold, Sihtric, of a Muslim expansion across Gaul and Germany - now that is magnificent! The bones of a strategy - a grand one - and in your engines there is the means to carry it out.’

The vizier stood and paced around the room, energetic, vigorous, red-faced. The servant cowered every time he came close.

‘I will continue the development of your engines, the crossbows, the armoured carts, the flying machines. And I will give them to the armies of Seville. Then, reinforced by our brothers the Almoravids from Africa, we will storm across the marches and scatter the barbarian hordes of the Christian kings. Perhaps our new conquest will be as rapid as that of Musa and Tariq - why not? And in five years, or ten, Seville will be established as the capital of a reclaimed al-Andalus, and the bells of the Christian churches will fall silent again.’ He continued to pace, pace.

‘And then?’ whispered Sihtric. ‘And then?’

‘And then we will cross the Pyrenees. We will reverse the disaster of Poitiers, three hundred years ago. This time there will be no stopping our advance.’