He said nothing of the second crusade, which had ended in disastrous failure only the year before, and I understood the reason for this and it brought me, if only for that moment, closer to Béroul than I was ever to come again: we were briefly united in the sorrow all Christians felt for our loss of Edessa, for our humiliation before the walls of Damascus, for the disorderly and ignominious retreat of the greatest army that the Franks had ever put into the field.

"We see further than they did," Béroul said after a moment of repose.

"Not because we have sharper eyes but because of the foundation they laid for us. They were giants, we are dwarfs. We see further because we are sitting on their shoulders. This is a figure of my own invention that I sometimes use when I want to explain these matters."

"It bears a resemblance to some words of Bernard of Chartres, written at a time before I was born."

"Well done, Thurstan! I made a little test for you. They have not exaggerated who praise your accomplishments. But I was intending to say that while the danger still lies in local practices, we see now today, here in Sicily, that the great threat to our Church is the existence among us of a militant faith hostile to our own. These Moslems are allowed to live and breed among us, their blood is corrupted, they will corrupt the blood of Holy Church, our blood." The calmer mood that had come to him when he spoke of those great men of the past was broken now, that fixed and staring look had returned to his face. "We will be condemned to live in our polluted blood and the words Ezekiel will come to pass."

"Is it to tell me this that you brought me here?" I said.

His eyes fell away from mine. He reached out a hand and moved his cup a little to one side, no more than a fraction, as if to find an ideal place for it. "You can help us in this sacred task. Your douana is a source of corruption. Will you say you have not noticed how year by year the language of the Saracens has supplanted all others in the documents produced by your douana? It was formerly Greek. Then Latin, the language of our religion, began to be used. But this was suppressed through their cunning. Now all is in their Saracen language. Will you say you have not noticed this?"

"It is not true that all is in Arabic. Greek also is used – my clerk is a Greek. Arabic is more usual now and the reason for that is not difficult to see. We use Saracen scribes because they have better instruction and write a better hand. We are occupied with land holdings and the grants and fees belonging to them. Clarity is essential. Those set to write in Latin could not make themselves clear in that or in any other language."

"Do you not see that this rise of their language is part of a conspiracy that goes far beyond the shores of this island? The Saracens ruled here once – not long ago. They are working to undermine the King's realm and to regain the power they had. They are assisted from abroad. Have you followed the rise of the Almohads in North Africa? One after another our colonies are falling to them, they are taking our ports and our trade, they are recovering the land for Islam. They send their spies across the water to stir up rebellion and acts of violence among their fellow-Moslems here."

He spoke as if no one else knew of these Almohads, the Berbers of Morocco who were taking all by storm, whereas most of Palermo knew of them, and all those in the palace service. I myself knew more about it than he did, as I had carried the King's money over the water to stiffen the resistance of the Emir of Bougie, who was favourable to our trade interests there, but all to no avail, every day our Arab friends were losing ground, these Almohads were already west of the Zurid Kingdom.

"They make use of the alamat to make secret signals among them," he said now.

"That cannot be true."

The alamat were a form of signature in the Kufic script used by Arab scribes in documents that circulated through the chanceries. "They are extremely difficult to read," I said. "Almost impossible."

"That is the cunning of it. They make the writing intricate not for the sake of ornament but so as to deceive. We have used trained scribes to decipher them. They are quotations from the Koran. Let me give you an example. 'On the Day of Judgement to whom will the Kingdom belong? To God, the One, the Victorious.'" He paused, staring across at me in a manner of one who has made a point impossible to refute. "It could hardly be clearer," he said. "That is an incitement to rebellion. Have you seen them pray? Hundreds of men moving together like a single beast."

I watched him in silence as he again paused to make a small adjustment to the position of his cup. His fingers were very white and the nails well cared-for.

"The Beast that waits to devour us," he said. "Who is it that gives your Saracen scribes their employment and oversees their work? Is it not the lord of your douana?"

"You know it is."

"Yusuf Ibn Mansur. He is close to the throne and seeks to come even closer. But he will not leave his place to you, Thurstan, he will leave it to a creature of his own. We know already the successor he has in mind."

If he was hoping I would question him on this, he was disappointed. In any case, I did not believe it. By spying we can find the nest of the lark, the lair of the fox, the place where a man hides his treasure. But the spy was not born that could see into the purposes of a man like Yusuf. Nevertheless, though confident of this, I felt stricken by Béroul's words as if they took some shelter from me. "I do not seek his place," I said, and this I felt to be true in the sense of actively seeking.

"We know certain other things about him. We know that he and certain others, Saracens subordinate to him, are engaged in perverting our faith by offering bribes to any that will convert to Islam."

This was so insensate a thing that for some moments I could not find words to answer him. By a law newly introduced by the Council of Justiciars – a council appointed by the King – such attempts at conversion, whether by bribes or coercion, were defined as a crime tantamount to treason. "But you are mad," I said at last.

"No, believe me, we have been watching him for a long time now. He has not made any such attempt on you?"

"No, of course not, never."

Béroul remained silent for some time, glancing away from me across the room. Then, still without looking at me, he said, "Think carefully, my fine young man. It is a capital offence. You would not want to be associated with him in guilt. It may be that you remember something, some form of words."

"What do you mean?"

"Something perhaps scarcely noticed at the time, but coming together afterwards in memory to form a particular significance."

Slowly he turned his face towards me and I saw the smile return and the attempted look of benevolence, which would always be defeated by the needy set of his jaws. "From you it would have great force," he said.

"Who came with evidence of this kind would earn the gratitude of some of the highest in the Kingdom, those able to grant any wish, able to change a man's life with a word, with the stroke of a pen."

My understanding of his meaning had been delayed by disbelief. It came now, leaving no room for surprise but only for rage. This was the urgent matter he had wanted to discuss, this was where that talk of Christendom had been tending. I got to my feet and looked down at him, feeling the rush of blood to my face.

"You dare to ask me to give false evidence against my benefactor? You think my honour so slight a thing?"

"No, no," he said. "I ask you only to search your memory."

He had not moved, which was fortunate for us both: if he had stood to face me, I think I would have struck him, even in holy orders as he was.