And a western empire, ruled by the 'plague-hardened' people of a 'Feathered Serpent', would learn of the rich lands across the Ocean Sea.

'They will come,' said Harry. 'Pushing across the Ocean Sea, a conquering fleet heading east where the Europeans might have gone west. On the coasts of England, France and Portugal they will fall on an overstretched Chinese empire.'

Abdul read,

The Feathered Serpent, plague-hardened,

Flies over ocean sea,

Flies east.

Serpent and Dragon, the mortal duel.

'But the western conquerors will unleash a horror not known in our continent since before the Romans.'

'"And Serpent feasts on holy flesh."'

'They eat the flesh of humans. They sacrifice human lives in great numbers. Their wars, Geoffrey predicts, will be terrible slave-raids, as captives from across a devastated Europe are hauled to their temples to die under the knives of the priests. Whole populations will be consumed…

'This, and no more,' Harry said. 'The prophecy lets us see no further.'

Abdul sat as if stunned. Then he got up and paced around the room. He took a bowl of jasmine blossom and breathed deeply of its scent. 'All this,' he said at last, 'if this Dove turns east and not west. But these final lines: "All this I have witnessed / I and my mothers." What does that mean?'

'Geoffrey says that Eadgyth was not a prophet, not a seer who could see the future, but – a puppet. The words were put into her mouth by a Witness, just as the line says, a saint of the far future – a woman, Eadgyth always believed – who will live at a time of the terrible calamity of the western invasion of the east, or at least fears its likelihood. And this person, wishing to avert the horror, will find a way – well, to speak to a woman of her own deepest past.'

'How?' Abdul demanded.

Harry smiled. 'If I knew that I'd sell it, and wouldn't be here talking to you. In fact, Geoffrey believes we are dealing with two prophecies here – or two witnessings. He says the Dove was meant to go west. Somebody else found a way to deflect him from his true course – somebody else has already meddled in history, and is trying to send the Dove the wrong way, east, equipped with the Engines of God. And it is a second witness who is now trying to reverse things through the Testament.'

Abdul thought that over, and laughed. 'Geoffrey says, Geoffrey says. These scholars are troublesome to men of the world like us. I suppose these Witnesses are scholars too, competing to muck about with history. And now we're meant to put it all right by packing the Dove off to the west?'

'That's the idea,' Harry said unhappily. 'I suppose the question is, what do we do now?'

Abdul sat again. 'I think we have a responsibility, even if the chance of the witnessing coming true is small, to try to avert this huge destructive disaster of the future of Serpent and Dragon. Anything would be better than that.'

'Agreed. So we must do something about it.'

'Yes. But you feel as uncomfortable about this sort of talk as I do, don't you, Harry?'

Harry shrugged. 'I'm just a merchant. I sell wool. That's all I know.'

'Yes.' Abdul gazed out of the window, and the dusty evening light caught the planes of his face. 'And I, I have always been outside the current of the world. I'm happy with that. Happy to observe, not to be involved. I'm content with my role here in the palace. In Granada, I'm trying to resolve problems, Harry. To save people. To restore equilibrium, if you like.'

'Not to change history.'

'Indeed. And yet here we are.'

Harry nodded. 'Where do we start?'

'We need to find this Dove of yours,' Abdul said firmly. 'For, it seems, all of history turns on his decisions. He must be a navigator, a mariner, a captain, or a ship-owner; he must be seeking sponsorship for his western voyages. These navigators all know each other – and are jealous of each other too. I will see if I can track him down.'

'And then what?'

'Then we will decide what needs to be done to send him on his proper way, off into the Ocean Sea.' He frowned. 'It occurs to me – this strange witnessing has fallen into the hands of our family. But families have a way of proliferating. What if there are others, Harry, others out there like you and me, likewise armed with the Testament of Eadgyth – or worse, the Engines of God? And what if one of those other unknown cousins has decided to work the other way – to send the Dove, not west, but east?'

Harry was appalled; that thought hadn't occurred to him. 'If so they will be looking for the Dove, as we are,' he said.

'True. We must keep our eyes open. And if we encounter them,' Abdul said calmly, 'we must deal with them.' And he pressed his nose to a jasmine petal, as if for comfort.

In the summer of 1485 Grace Bigod, with Friar James in tow, travelled back to Spain. Grace wanted to press her case for the adoption of the Engines of God by the Spanish court.

But the Spanish were at war. This year, Fernando and Isabel were engaged in the siege of a Moorish town the Christians called Ronda.

So James and Grace travelled across the country to Ronda with a raiding party of Castilian soldiers. Moving inland from the coast they crossed a landscape of folded hills and flood plains through which rivers snaked, glistening, and fortified towns sat squat on the hilltops. The scars of the monarchs' war were everywhere, in the burned-out fields, the hulks of abandoned farmhouses, the stinking carcasses littering the roadsides.

The knights called themselves caballeros, and they were attended by hidalgos, lesser nobles. As they rode they joked, sang and drank. James thought they had a certain lazy arrogance. If they saw a stone wall standing they would run their horses at it to knock it down, if they saw a haystack they would torch it, if they saw a well they would throw stones down it to block it up, if they saw an irrigation channel they would dam it with dead cattle. With their crusaders' crosses stitched to their sleeves they dedicated each new bit of destruction to Saint James the Moorslayer, and they dreamed of what they would do if they found a few plump Moorish women hiding out in the ruins. Thus they wrecked a landscape that had been intensively farmed for seven centuries.

Grace had no sympathy for James's unease at all this. 'You're a hypocrite,' she said bluntly. 'You gladly devote your pious, pointless little life to the development of devastating weapons. And yet you flinch when you see the results.'

James faced his conscience, and he knew she was right. He had had no choice about being assigned by his abbot to the engines project. But he was thirty years old now, and as the years had worn away he had become engaged in the intellectual exercise of the engines for its own challenge. It was thrilling to see these most remarkable toys emerge from heaps of wood and iron, saltpetre, sulphur and carbon – a thrill, his confessor warned him, that might be a compensation for other aspects of his life that he had piously put aside.

But he had, he realised, built a wall in his mind between the development of the engines and their ultimate purpose.

He said unhappily, 'It's just that I didn't expect it to be like this.' He waved a hand. 'Is this war? This wanton destruction of property – there will be famine here in the winter – this savagery inflicted on the old and the ill, on women and children.'

She laughed at him. 'What did you expect, chivalry? You ought to read a little more widely, brother. This is the way wars are fought now: French against Flemish, Italian against Italian, Moor against Christian… Why, we English pioneered the technique, in our long war with the French. You cut off your enemy at the knees by removing his food supply, by shocking his population into terror and submission. There's even a word for it, I'm told: chevauchee. Wars are fought like this all over Europe now, like it or not.