‘I have always “tinkered”,’ Bacon said. ‘I once set up a candle and a mirror in a darkened room, and peered into the eye of a cat. Have you ever tried such a thing, brother Saladin?’

‘I can’t say I have.’

‘You see a carpet of dusky red vessels overlaid by a golden tracery. Quite beautiful, quite mysterious. My study in optics began with those first observations. And if you could look into the head of a man, what would you find? But I have never been able to persuade anybody to sit still long enough to let me see. Ah, well.’

‘I thought all truth was to be found in the Bible.’

‘Of course, and in the authorities of antiquity. I myself am one of Europe’s leading scholars on Aristotle,’ Bacon said without a shred of modesty. ‘But there are many routes to the same destination, which is God’s truth. The role of the natural philosopher is to understand how phenomena reveal that truth. Saint Augustine himself instructed us not to embarrass ourselves by quoting the word of God to contradict some fact of nature, because that would only reveal that we understood neither the word nor the nature. Experimentation: that is the way to that deeper truth, that final reconciliation. Or so I am coming to believe. Perhaps you have heard of the work of Master Peter de Maricourt, a Picard who once took the Cross, and subsequently—’

‘Yes, yes, Roger,’ Thomas cut in. ‘But perhaps we should get to the point?’

Bacon smiled, utterly in control. ‘Quite right, Father, quite right. You!’ He jabbed a finger at the novice, who jumped. ‘More wine for our guests. And bring a lamp over here.’ He sat before the low table, opened his leather wallet and extracted papers that he proceeded to spread out. ‘We have a deep mystery to unravel.’

Saladin murmured to Thomas, ‘He’s quite a showman, isn’t he?’

‘And he knows it. But it’s not necessarily good for him. Ah, Roger, Roger, how your busy head distracts your pious heart!’

But they sat before Roger Bacon, wide-eyed, as he began to reveal the truth of the Incendium Dei cipher.

XXI

XXI

‘We begin with your fragment of coded text, as Thomas presented it to me,’ Bacon said. He spread out a parchment on the table:

BMQVK XESEF EBZKM BMHSM BGNSD DYEED OSMEM HPTVZ HESZS ZHVH

‘I was intrigued by the puzzle . . .’

‘I knew he would be,’ Thomas whispered to Joan. ‘Very useful thing about scholars, that curiosity. He didn’t even ask for a fee.’

Bacon glanced at Saladin. ‘You. Tell me what you see.’

‘I’m no scholar—’

‘Just answer.’

‘I see ten words,’ Saladin said. ‘Latin letters, not Arabic. I recognise none of the words, though.’