‘Not the devil,’ Grace said smoothly. ‘It is all the work of man, his imagination divinely inspired.’

‘But how is it possible for such a weight even to drag itself over the earth? There must be a herd of horses in there.’ He cupped his ears in gloved hands. ‘And the noise—’

‘Not horses. Bacon’s black powder.’ And, sitting beside Ferron in the wooden viewing stand, she tried to explain how the gunpowder had been harnessed into an engine. ‘There are a series of pistons. When the gunpowder charge explodes above each piston, air is forced out of a chamber of iron, and the piston is dragged up, as a man inhaling may draw a feather into his mouth. That motion is translated into a turning of the great wheels, by a complicated mechanism James could no doubt describe for you. And so the steel beast travels forward, powered by a beating heart, each pulse a detonation that could kill ten men . . .’

While Bartolomeo Colon stared, fascinated, it seemed to be too much for Ferron. He held his hands over his ears, flinching from each new explosion. ‘Devilish,’ he repeated. ‘Devilish.’

She tried to distract him with the manufactory’s new sort of arquebus; one of them was set up on display before them. ‘Then consider this, brother. The old sort of hand gun, as Isabel is deploying against the Moors even now, is slow to reload, and unreliable to fire, for you must apply a flame to the powder that propels the shot. Now we have a new sort of gun - based, again, on the designs in the Codex - which is fired not by flame but by a spark.’ She showed him how, when a trigger was pulled, a hammer slammed a bit of flint against a steel plate; the resulting sparks were funnelled into a chamber to ignite the gunpowder.

Ferron was distracted by the glistening mechanism as she operated it. ‘I see,’ he said. ‘I see.’

‘It is still difficult to reload - we will work on that - but the reliability is so much improved, the weapon is so much safer, that it will be as if we have double the number of soldiers in the field. And furthermore—’

‘What,’ Ferron said, pointing, ‘is that?’

It was a woman - young, scrawny, dirty. Grace had no idea who she was. She was running. She fled towards the battlefield. Grace could not have imagined a more unexpected sight.

And now monks followed her, grimy, blinking in the light. They too ran towards the noise and smoke of the field, not pursuing the girl, just running. But one of them called over his shoulder to the spectators in the viewing stand. ‘The manufactory! Get away, my lady - the manufactory!’

‘Dear God,’ Ferron said.

Grace was bewildered, unable to understand what was happening. ‘I think—’

The explosion was a roar, all around her. She was thrown forward onto the ground, helpless as a doll.