‘You will thank her for me,’ Guinevere said and then, despite the cold, she went and pushed open the shutters of a window so that daylight could come into the room. The fire swayed under the rush of cold air and sparks whirled up to the blackened beams. Guinevere was robed in thick brown wool. She was pale, but that haughty, green-eyed face had lost none of its power or pride. ‘I had hoped to see you sooner,’ she chided me.

‘It has been a difficult season, Lady,’ I said, excusing my long absence.

‘I want to know, Derfel, what happened at Mai Dun,’ she said.

‘I shall tell you, Lady, but first I am ordered to give you this.’I took Arthur’s parchment from the pouch at my belt and gave it to her. She tore the ribbon away, levered up the wax seal with a fingernail and unfolded the document. She read it in the glare of the light reflected from the snow through the window. I saw her face tighten, but she showed no other reaction. She seemed to read the letter twice, then folded it and tossed it onto a wooden chest. ‘So tell me of Mai Dun,’ she said.

‘What do you know already?’ I asked.

‘I know what Morgan chooses to tell me, and what that bitch chooses is a version of her wretched God’s truth.’ She spoke loudly enough to be overheard by anyone eavesdropping on our conversation.

‘I doubt that Morgan’s God was disappointed by what happened,’ I said, then told her the full story of that Samain Eve. She stayed silent when I had finished, just staring out of the window at the snow-covered compound where a dozen hardy pilgrims knelt before the holy thorn. I fed the fire from the pile of logs beside the wall.

‘So Nimue took Gwydre to the summit?’ Guinevere asked.

‘She sent Blackshields to fetch him. To kidnap him, in truth. It wasn’t difficult. The town was full of strangers and all kinds of spearmen were wandering in and out of the palace.’ I paused. ‘I doubt he was ever in real danger, though.’

‘Of course he was!’ she snapped.

Her vehemence took me aback. ‘It was the other child who was to be killed,’ I protested, ‘Mordred’s son. He was stripped, ready for the knife, but not Gwydre.’

‘And when that other child’s death had accomplished nothing, what would have happened then?’ Guinevere asked. ‘You think Merlin wouldn’t have hung Gwydre by his heels?’

‘Merlin would not do that to Arthur’s son,’ I said, though I confess there was no conviction in my voice.