The archives were housed in a gloomy stone building at the back of the square. They entered by a gate in a stone wall, and walked up a gravel path to the main door, past beds of rose bushes that had long since ceased to flower. Only the thorns remained.

Nick turned a heavy iron ring on the door and was admitted to the reception area. Nothing in the exterior had prepared him for it: instead of oak floors and ancient furniture, he found himself in a corridor with a linoleum floor and strip-lighting. A woman in a severe black skirt-suit sat behind a desk, underneath a poster in a plastic clip-frame.

‘Bonjour,’ said Nick. He turned to Emily. ‘Do you want to explain?’

‘I speak English,’ the archivist announced without looking up. She kept writing. ‘Can I help you?’

‘We’re interested in the library of the Count of Lorraine,’ Emily said. ‘We were told that it became part of your archive.’

A look of surprise broke the archivist’s scowl. She put down her pen. ‘You are the second person in a month to ask me about the Comte de Lorraine. Etrange.’

‘Who was it?’ Nick demanded. The archivist gave him a blank look. ‘Was it a woman, tall and thin with red hair?’ He pulled out his wallet and fumbled among the cards for the battered, passport-size photograph that he’d never got round to removing. Just in case. Next to him, he caught a sideways glance from Emily.

‘Was this her?’

The archivist pursed her lips in confusion. ‘Oui. C’est elle. But blonde.’

‘Do you remember when she came? The date?’

The archivist watched him through narrowed eyes. ‘Do you have her name?’

‘Gillian Lockhart.’

She flipped through a ledger that lay open on the desk, a register of names and dates and scribbled signatures. There hadn’t been many. Two pages back, Nick spotted it. The familiar shape, the bold G and the brisk lines that followed. A very masculine signature, he’d always thought.

He read the date in the left-hand column beside her name: ‘December 16 ’. She must have come here almost straight from Paris. Nick’s heart raced with more hope than he’d felt in a week.

‘And did she find it? The book she was looking for?’

A sigh. ‘I tell you the same as I have told her. The books of the Comte de Lorraine came here in the century of the eighteen hundreds. You know the history of Strasbourg?’

Nick shook his head.

‘In 1871, we are attacked by the army of Prussia. They surround the city and they bombard it. Much of the city burns – including the great library. Some books survive – but of the Comte de Lorraine, there is not.’

Strassburg

Often the fates drag us down like ocean waves and all our toils count for nothing. But sometimes, rarely, they rush us aloft on currents so quick even angels would struggle to keep pace. Such was my experience in those golden months in Strassburg. With Dritzehn’s money, I paid off my old loans and restored my credit. That allowed me to take out new loans, on better terms, to buy metals for our project – which in turn stood as collateral for another round of loans. Those bought more metals, which funded more loans – and so again, a virtuous circle. Of course there was little income in those months to repay the loans, but I had allowed for that. I had agreed that the interest would be added to the principal and none of it fall due until October of the following year, once the mirrors were sold in Aachen. Then, armed with the profits, I could turn my efforts back to the indulgences.

Some nights I dreamed that I sat atop a giant tower of mirrors stacked halfway to the sky, swaying and bending like a rope end in the breeze. The height made me dizzy; I knew that a single gust of wind might topple the whole tower and shatter it in ruin. But it never did.

Manufacturing the mirrors required two separate processes. The latticework frames had to be cast from the alloy, and the steel mirrors polished to a high reflective sheen. Eventually, the one would be attached to the other by means of clips, but we agreed this should be done as late as possible. When spring came we would hire a barge to carry our cargo down the Rhine to Aachen, and we did not want the mirrors scratched in transit. None of us knew how that might affect their holy properties. So we cast the frames at St Argobast, where I had the forge, and used Dritzehn’s house for the mirrors.

Late that September, the fates moved again. I had spent the day in Strassburg, arranging delivery of the next batch of metals and assuring my creditors that all was proceeding apace. The sun was edging towards the horizon, but I did not have to hurry. I made the journey between my house and the city so often in those months that I had acquired a horse, a docile mare I named Mercury. So I decided to visit Dritzehn.

I was just approaching the house, picking my way around two dogs squabbling over a piece of offal that had fallen from a butcher’s cart, when I heard a loud voice behind me.

‘Johann?’

It was not uncommon to be hailed on the streets. I had been in Strassburg almost four years and my name was well known, if only because I owed so many of its citizens money. What struck me was the surprise in the voice, the force of long-lost recognition. I had no long-lost friends I wanted to see again.

I turned, dreading who might be there. At first I did not recognise him. The last time I saw him he had been young and fit, overflowing with energy. Now his face was lined, his hair greyed far more than mine. He walked with a cane, dragging one leg behind him. Yet whatever misfortunes had blighted his life, they had not dimmed the essential fire that animated him.

‘Aeneas?’

He beamed. ‘It is you. I was certain of it. You look as if the years have treated you well. Unlike me.’

I glanced at his withered leg.

‘What happened?’

‘I went to Scotland.’ He grimaced. ‘A barbarous place. I almost died. Then my ship sank and I had to walk home.’

It must have been terrible, but he said it with such relish that I had to laugh. ‘You almost died the day I met you,’ I reminded him. ‘You should take more care of yourself. But why are you in Strassburg?’

‘I am supposed to be meeting some priests from Heidelberg. I think they want me to spy on the Pope.’ He winked. ‘But I am Italian; they will expect me to be late. The last time I saw you we agreed to meet in a tavern. I did not think it would take six years to get there, but I am happy I have found you at last. Will you share a drink with me?’

I had been wrong. There were faces from my past I was happy to see.

I led him to a wine cellar near the river, one I had never visited before. I wanted to avoid any place that Drach might see us together, Somehow, he and Aeneas belonged to separate parts of my life. I did not want them to meet.

Aeneas raised his glass and toasted me. ‘You are an extra-ordinary man, Johann. You emerged from that river mud fully formed, and vanished like a ghost. Now here you are, by your attire apparently a prosperous merchant. “Varium et mutabile semper,” as the poet says. Always changeable and surprising.’

He fixed me with his familiar gaze, eternally hopeful and inquisitive.

‘I’m sorry I abandoned you so suddenly,’ I said. ‘I had to go.’

Aeneas waited for more. When he saw he would get none, he nodded. ‘I suppose even men who emerge from the mud have pasts. Perhaps some day you will tell me how you came to be there.’

I changed the subject. ‘And Nicholas? How is he?’

Aeneas looked sad. ‘We do not speak so much now. You know that the Pope has just dissolved the council of Basle?’

I did not, though I knew that it had continued until recently. Every few months I heard some news of it in church or in the marketplace, and was astonished that the council I had briefly participated in six years earlier still ground on.