‘Keep low,’ Gillian whispered.

‘I thought you said this place was empty.’

‘No point taking risks.’

They crawled along the wall, keeping below the rim of battlements, until another flight of stairs brought them down to the courtyard. They skirted its edge, keeping in the shadows around the storehouses and sheds, under a trellis of withered vines and past a stone well. Tyre treads and footprints gouged the snow; Nick wondered how fresh the marks were.

He was so busy looking ahead for danger that he didn’t watch his footing. He kicked against something, tripped and fell forward. He pushed himself up on his hands.

A three-eyed monster, like some horror from the bestiary, stared at him out of the snow. Its skin was stippled blue and black, its lips locked in a silent scream. Nick opened his mouth, but no sound came out of his frozen lungs. He scrambled back, caught his knee on something else and rolled over. Face to face with another monster.

They were monks. Two more of them, each with a single bullet hole drilled in his forehead. There was less blood this time: the cold and snow must have frozen it almost instantly.

Nick got up. ‘We really need to get out of here.’

Even Gillian looked frightened now. But she’d always thrived on proving she could do what others were afraid of. Before Nick could stop her she’d run along the foot of the wall to a doorway into the keep, turned an iron ring and opened the door. Nick cursed and followed.

‘Don’t they lock anything around here?’

‘The only way into the castle – the only way they know about – is across a drawbridge over a hundred-foot gorge. It’s worked for five hundred years.’

As she said it, she led them across a corridor and flung open a pair of double doors. Nick and Emily stared.

It was like a cathedral built of books. Gothic pillars eight feet thick rose to a dimly raftered ceiling high above. All the space between was filled with shelves, and every shelf was jammed tight with books. Every storey or so wooden galleries emerged, snaking around the pillars and in front of the shelves like the canopy of a forest. The floor mirrored the image back: interlocking swirls of many woods, inlay on a giant scale, twisted in scrolls like foliage.

‘The Bibliotheca Diabolorum. The Devils’ Library.’

As they advanced into the room, Nick saw that the books weren’t free on their shelves, but locked behind a lattice of thin wire bars. Some looked impossibly ancient, with varicose cords running through their spines; others had the split cloth and frayed edges of old school books. The whole room was suffused with the musty smell of old paper – and something more acrid. Gasoline?

Emily peered through the bars and examined the names on the spines. She shuddered. ‘No wonder they call this the Devils’ Library. Pretty much every book ever written about the black arts is here. And some I’ve never heard of.’

‘There’s a reason for that,’ said Gillian over her shoulder.

She walked quickly to the back of the room. The smell of gasoline was stronger here and some of the books looked damp. Before Nick could wonder why, Gillian was reaching for a small leather book, almost invisible between the massive volumes around it. To Nick’s inexpert eye the books here looked older than in the rest of the room: he was surprised there was no grille protecting them. A second later he saw why. The book rattled as Gillian withdrew it. When it came free, Nick saw a heavy chain anchoring it to the wall. Most of the links were black with age, though one gleamed steely fresh.

‘Bolt cutters,’ said Nick, remembering her list.

‘I don’t suppose you brought any. They took mine away.’

Nick’s brain ached from trying to keep up. He didn’t know who he’d thought he’d come to rescue, but it wasn’t this incarnation of Gillian, who strode around forbidden castles as if she owned them. He’d have taken more care in a video game.

‘Who are they anyway?’

‘The Church? The mob?’ Gillian shrugged. ‘The Italians have only managed to organise two things since the Roman empire: the Catholic Church and the Mafia. I guess it’s not surprising they work together.’

‘But why-’

Gillian rested the book on the shelf and slid it across.

‘Take a look.’

LXXXII

Mainz, 6 November 1455

Fog came down in the night. When day dawned, the city had disappeared. From my bedroom window I could not even see the house opposite, except for the tip of its roof looming from the mist like a ship’s prow. I pulled on my fur-trimmed coat and remembered the youth who had dressed in this same room thirty-five years earlier, waiting for a court to tell him he was insufficiently well born to inherit his father’s estate.

The house was empty. I had told the others, those who stayed with me, not to come to work today. Even the servants were gone. I had not asked Kaspar to leave, but when I looked in his room he was not there. Part of me was disappointed, another part relieved. I drifted around the lonely house, too dispirited even to rouse a fire. I should have been working on some sort of defence for my trial, but each time I thought of it a great dread crushed my soul.

I went into the workshop and looked at the press. It stood in the middle of the room like a gallows, the platen raised, the ink tables dry, blank piles of paper stacked beside it. I ran my hand over the rugged frame. I pressed my fingers against the type in its bed and looked at the red indentations it left in my skin. I felt as I had that morning in Paris – void. I had stared into the flames and conjured the rainbow. Now all that remained was ash.

But I also remembered that day in Paris was when I first encountered Kaspar’s art. I went to my bedroom and took down his bestiary from its shelf. I leafed through the well-thumbed pages, marvelling again at his skill. Many of the beasts looked almost human: the shy deer with its chin tucked against its breast; the lovelorn unicorn who stared at the virgin maid and did not see the hunter’s net behind him; the bonasus who roasted his pursuers with fiery dung and mischievous glee.

I turned to the last page to look at the card, the four bears and four lions who had led me so far.

Written by the hand of Libellus, and illuminated by Master Francis.

He also made another book of beasts using a new art of writing.

I blinked. A second sentence had been added to the colophon, written in a hurried hand in watery brown ink. It was Kaspar’s writing. He must have come straight from the press when he wrote it, for he had dripped press ink on the card below.

‘I wondered when you would find my note.’

A tremor ran through me. Kaspar had appeared, silent as a devil, standing in the doorway and watching me with a crooked smile. I held up the book.

‘What does this mean?’

‘What it says.’

He stepped out of the shadows, revealing a slim leather-bound book in his hand. He gave it to me.

‘A gift.’

My hands trembled as I opened it.

Nick’s hand trembled as he opened the book. A second later, he felt unexpectedly deflated, an echo of how he’d felt in the hotel room in Paris, opening Gillian’s envelope and laying eyes on the card at last. The first page was utterly familiar – a cleaner, clearer version of the page the computer had stitched together for them in Karlsruhe. The bonasus with the wicked grin, spraying its fiery excrement over the men behind it: a monk, a knight and a merchant.

‘The lion is the strongest of all beasts and fears nothing.’ Gillian reached across him to turn the page, brushing against him as she did. Nick flinched away. ‘But how much braver is the worm, weakest of creatures, in constant fear he may be crushed yet humbly scavenging among the footfalls of giants and monsters. In time, he brings low even the noblest beast.’