‘The council was finally beginning to achieve something. There is so much rotten with the Church, and it all starts at the top. The council had taken some sensible measures to reform the worst abuses. Naturally, this involved curtailing the Pope’s power. We – the council – needed to assert that the Pope is a servant of the community of the Church, not its master.’

He spoke animatedly, rocking on his stool as he talked and catching my eye often to be sure I agreed. I tried to look noncommittal; that only stoked his enthusiasm.

‘The Pope, jealous of his position, dissolved the council in Basle and ordered it to reconvene in Italy. By having it closer to Rome, he hoped to bring it to heel. Many members obeyed: but those of us who see how the Church must be reformed refused. We stayed in Basle and voted to suspend the Pope, who has at last shown his true colours.’

‘Nicholas went to Italy,’ I guessed.

‘He has his reasons. I cannot agree with them. He wants the Church unified; I want it perfected.’ Aeneas stared at the table dejectedly. Then, suddenly, a smile flashed across his face. ‘More to the point, it is the men in Basle who pay my wages.’

I do not know what ever happened to the priests from Heidelberg who hoped to meet him. We sat in the tavern some hours, emptying cups of wine and plates of food. As always, Aeneas talked most, but I was happy to listen. He was easy company. Conversation with Kaspar was a field of swords: no statement went unargued, no compromise or trivial hypocrisy unwithered by his sarcasm. I never knew when the idlest comment might be hurled back at me – or wound him so unexpectedly that he would spend the entire evening sulking. It was exhilarating, but also exhausting.

Aeneas, by contrast, prided himself on neither giving nor taking offence. In this he was only intermittently successful: his love of speech was so great that words often outpaced tact. But he always recognised his mistakes, with such sincere contrition that it was impossible not to forgive him.

‘It is good to see you looking so well,’ he told me. I believed it: he always took genuine pleasure from those around him. ‘Are you married?’

Some memory of the disaster with Ennelin must have shown on my face. Even before I could demur he hurried on. ‘For myself, I am lately in love. Smitten. There is a woman at the inn where I am staying – Agnes is her name – from Biscarosse. The most sublime creature.’

Despite myself, I was drawn into his story. ‘Is she travelling alone?’

‘Her husband is a merchant. He leaves her there while he travels up and down the river to contract his business. I saw him at breakfast two days ago. He is a fool. He does not deserve her.’

‘Is this how you plan to reform the Church? By seducing other men’s wives?’

Aeneas gazed on me with a soulful look. ‘I could never take the vows of a priest. She ravished my heart with a single glimpse. Do you see these bags under my eyes? I cannot sleep because of her. Every night I go to her door and plead with her, but she is cool and steadfast as marble. She does not admit me – yet she gives me reason to hope. Perhaps tonight I shall finally conquer. I must, for tomorrow I return to Basle.’

He dropped his head like a dog. ‘I know this love is ruinous. But I would rather this agony than a lifetime of numb comfort. Can you understand that?’

‘I understand,’ I murmured, and the longing in my voice must have penetrated Aeneas’ self-pity. It drew a swift glance.

‘I will not ask,’ he said. ‘You never tell me anyway. But I hope we both win our hearts’ desires.’

I raised my glass to that.

‘And now I must go.’ He stood abruptly. In another man it would have been discourteous; with Aeneas, it signified only that his busy mind had leaped forward again. ‘I must sleep now if I am to woo my Agnes tonight.’

I was sad to part. He had reminded me of a simpler age in my life, a humble time when all that mattered was faithfully copying what Nicholas said. Also how wretched I had been before he rescued me. All I had repaid him with were sudden disappearances and evasions. I owed him more; I wanted him to know my gratitude.

‘I am sorry about Basle.’ I pulled the mirror out of the pouch on my belt. It had become a talisman for me in those golden months, proof of our good fortune. I carried it everywhere. ‘I never forgot your generosity.’

His face lit up with delight. He embraced me. ‘I am glad I found you. I hope you do not disappear again.’ He took the mirror from my hand and examined it, smiling. ‘My Aachen mirror. I had almost forgotten it. I do not know that it ever brought me good fortune, but perhaps it averted some great misfortune that would otherwise have befallen me. Perhaps I stood too far away to feel the full effects of the rays.’

He handed the mirror back. ‘I have just returned from Aachen, actually, on an errand for the council.’

‘Is all well there?’ I asked, feigning carelessness. I had not told him the secret of the mirrors. ‘Is all in hand for next year’s pilgrimage?’

‘It is a disaster.’ Aeneas began to turn away, eager to be back to his inn. ‘Has the news not reached here yet? An outbreak of the plague has swept the north. No one knows when it will end or how many souls it will claim. The authorities in Aachen have had no choice but to postpone the pilgrimage for a full year.’

He peered at me through the deepening gloom. ‘What is wrong, Johann? You look as though you are about to disappear again.’

Strasbourg

They checked into a hotel near the cathedral. Nick felt deflated, utterly empty. Once again he had caught a glimpse of Gillian; once again she had vanished.

‘I’m going to look around the town,’ Emily announced. ‘Would you like to come?’

‘I’m not interested in sightseeing,’ Nick growled. But when he threw himself down on the hotel bed, he found he couldn’t sleep. After two minutes he hurried downstairs and caught Emily in the lobby, just about to leave.

‘Changed my mind.’

They stepped out. Although it was early afternoon, the sky was dark. The yellow lights in the hotel windows glowed warm behind them. A thin layer of snow already dusted the street, and looking at the pregnant clouds Nick guessed there was more to come. When he looked back at their footprints they seemed small and lonely, like two children lost in the woods.

He pulled his coat around him. ‘Where are we going?’

‘The cathedral,’ said Emily. ‘There’s something I want to see.’

They walked up between black and white rows of half-timbered houses and passed through the cathedral’s west door. It was so dark inside that Nick thought for a moment it must be closed – darker even than the day outside. All he could see was glass, spectral-coloured images floating above him, dizzyingly high. For a moment, he shared the awe the medieval congregation must have felt as they entered the sanctuary, the sense of a half-glimpsed heaven above.

The darkness disoriented him. He reached out in the gloom and touched Emily’s arm to reassure himself she was still there. She moved closer, as if glad of a human connection in the face of the medieval God’s icy grandeur.

Nick pointed up to the north wall, where a line of larger-than-life men stood proudly in the glass. ‘Who are they?’

‘The Holy Roman emperors. It’s one of the most famous compositions in medieval glass.’ She made a little harrumphing sound. Nick couldn’t see her, but he knew the frown of concentration that went with it.

‘What are you thinking?’

‘The kings of Israel.’ Nick wasn’t sure if she was speaking to him or the darkness.

‘I thought you said they were the Holy Roman emperors.’

‘The kings of Israel were another popular motif in medieval art. The facade of Notre-Dame in Paris was decorated with twenty-four statues of them. There’s also the Dom in Cologne, which has forty-eight kings in the stained glass of the choir, I think. They’re assumed to be the twenty-four kings of Israel and the twenty-four kings from the Book of Revelation.’