‘I’m an auctioneer. But I’ve got friends in the Art Squad at Scotland Yard. Sometimes I do them the odd favour. A few months ago they asked me to keep an eye on Gillian. Things had been going missing from the Cloisters in New York and turning up for sale in London, but the museum could never prove anything. In the end they wrote her a first-class reference and packed her off to Stevens Mathison. Soon afterwards it started happening to us.’

Nick jerked his thumb at Royce. ‘Was he involved?’

‘Only when you showed up in Paris.’ Royce flashed him a grin: it looked less unpleasant than it had in the interrogation room. ‘Simon called London, who of course had the heads-up on you from Interpol. They called me. I got that special feeling I get sometimes. Instead of booking you for murder and obstruction of justice, I figured we might get something interesting by following you.’

‘And Atheldene? Almost getting killed in Brussels? Was that part of the plan?’

Atheldene played with the button on his coat. ‘That was genuine. I was terrified. I usually get called in to tell the Art Squad when someone’s selling something they’re not supposed to own, or to see if the object in an insurance claim is genuine. I’m not used to this sort of thing.’

The helicopter banked around the mountain. The clouds had parted and a cold moon appeared.

‘What’s that?’ Atheldene pointed to the hillside below. A fire burned among the trees, a golden bead in the silver forest.

The pilot’s voice, German accented, came over the headsets. ‘Maybe a car crash? I call Oberwinter to send the police.’

‘Can they send a fire engine too?’ Atheldene craned around so that he could see the castle. The roof must have collapsed: the flames now rose unhindered out of the shell of the tower.

‘On that road, it is not possible. Maybe in the morning.’

‘The Devils’ Library,’ Atheldene murmured. ‘Imagine even half an hour in that place.’

‘I’d have swapped with you,’ Nick muttered. ‘You wouldn’t have liked the librarian.’

‘Point taken. But it is a shame about all those books.’

Emily reached inside her shirt and pulled out a battered brown-leather-bound book.

‘Not all of them.’

Atheldene almost lunged for it across the cabin, then remembered his manners. ‘Is that the one…?’

‘No. It was chained to the wall – I couldn’t. But I managed to grab this. Anyway, I prefer it.’ She passed it to Nick. ‘It’s for you.’

Nick shook his head. In the back, he could see Gillian breathing fitfully as she slept under a blanket.

‘I got what I came for.’

What I say to you in the dark, tell in the light; and what you hear whispered, proclaim from the housetops.

It was strange to be back in the Humbrechthof. The clatter of the presses; types clicking together in their sticks; the shouts and banter of the apprentices calling across the yard for more paper, more ink, more beer. But it was no longer mine. The purpose that animated the house had changed: practical, routine, no longer charged with the excitement of discovery. Kaspar and I, Götz and Keffer and the others, we had charted a new country. Now a second generation had arrived to lay down roads and barns, drain marshes, plant crops, tame the wilderness. Many of the faces I saw were new: they glanced at me as I passed, but only idly. A few recognised me, and looked away or shook my hand as their consciences allowed. Peter Schoeffer was not among them.

‘He went to Frankfurt,’ said Fust, when he received me in his room. ‘He has some business there with a bookseller. He should have returned by now. He will be sorry to have missed you. No doubt some woman delayed him.’

I let the lie stand, and wondered if Fust knew that Schoeffer was sleeping with his daughter. Fust misread my expression.

‘He thought the world of you. As an artist, as an inventor. Nothing pained him more than having to choose between us. He is my heir, but yours also.’

He picked up a small block of engraved metal from his desk and gave it to me. It came apart in my hands: I began to apologise, then realised it was meant to. One part, the smaller, was a bulbous letter B, intricately carved so that within the strokes of the letter itself flowers grew, branches blossomed and a hound chased a duck over a meadow. It fitted into a slot in the second piece of metal, engraved with a lush border of foliage, to make a seamless whole.

‘Peter’s invention. You ink the inner part red and the outer blue, then drop it in among the black-inked forms and print the initials. We are using it on a psalter for the cathedral.’ He showed it to me imprinted on a piece of paper, sharper than any illuminator or rubricator could produce.

‘Beautiful,’ I admitted. Perhaps I had been wrong. Perhaps there were still discoveries to be made in this house.

‘It is still too slow. Peter is like you that way, obsessed with quality and no thought to cost.’

An awkward silence hung between us. Fust escaped it by shuffling papers on his desk until he found the one he sought.

‘I suppose we should finish our business.’ He gave me the document to sign and seal. ‘I am sorry this is necessary. The psalter is late; the Church is slow to pay, so I must borrow more money. The Jew had heard about our disagreement and demanded an assurance that you accepted all the terms of the court’s judgment. It is only a formality.’ He lit a candle and reached for the sealing wax.

‘You will forgive me if I am cautious about anything you give me to sign.’

‘Of course.’ A sharp-toothed smile. I could not wound him so easily.

I read it through. Fust took the contents of the Humbrechthof, the presses and types, the ink and paper, the furniture, down to the last composing stick. He also kept the finished Bibles to sell at his own profit. The Gutenberghof, its press and everything in it remained mine. There was a time when I had burned with the injustice of it; now my anger had cooled. It was past.

I signed my name at the bottom and pressed my seal into the soft wax. Punch and form. Fust did the same.

‘You have a new seal,’ I noticed. A black bird with a yoke around its neck, supporting two black shields blazoned with letters and stars.

‘The Fust and Schoeffer Book Works. Peter designed it. We will stamp it in all our works, a hallmark of our quality. Customers will demand nothing less.’

I did not like it. In its way, it seemed a greater blasphemy than anything Kaspar ever did. To put your mark on a piece of art, to claim it for your own, was to appropriate it from God.

Again, Fust misinterpreted my frown. ‘I am sorry,’ he repeated. He wanted me to believe it. ‘The street between our houses is not so very long. No doubt we will see each other. I hope we can be friends.’

I was old enough that it barely hurt to lie. ‘I hope so. But not now. I am leaving Mainz for a time.’

There was no missing his relief. ‘Where will you go?’

‘I have an errand in Strassburg.’

April sunshine bathed the city. The half-timbered houses and Gothic turrets shone with a warm light; bright colours festooned the square where racks of tea towels, postcards and guidebooks had sprung up like spring flowers. Crowds of tourists milled about, enjoying the Easter holiday, while kings and angels, lions, knights and serpents watched from the stone above.

No one paid any attention to the young couple who walked hand in hand across the square. They entered the cathedral by the west door, under the monumental facade, into the deep twilight that kept perpetual hold on the interior. To their left, on the north wall, a row of stained-glass kings glowed vivid with the light behind them. Nick’s pulse quickened; he squeezed Emily’s hand.