‘Come this way.’

Leonardo’s smaller, inner room was even more untidy than the studio, but among the masses of books and specimens, and papers covered with that indecipherable scrawl, the artist, as always (and incongruously) impeccably dressed and scented, carefully piled some stuff on other stuff until a space was cleared on a large drafting table.

‘Forgive the confusion,’ he said. ‘But at last we have an oasis! Let’s see what you’ve got for me. Unless you’d like a glass of wine first?’

‘No, no.’

‘Good,’ said Leonardo eagerly. ‘Let’s see it, then!’

Ezio carefully extracted the blade, bracer and mechanism, which he had previously wrapped in the mysterious vellum page that had accompanied them. Leonardo tried in vain to put the pieces of machinery back together but failed, and seemed for a moment to despair.

‘I don’t know, Ezio,’ he said. ‘This mechanism is old – very old – but it’s very sophisticated as well, and its construction is ahead I would say even of our time. Fascinating.’ He looked up. ‘I’ve certainly never seen anything like it. But I’m afraid there’s little I can do without the original plans.’

Then he turned his attention to the vellum page, which he had picked up in order to wrap Ezio’s pieces back up again. ‘Wait a second!’ he cried, poring over it. Then he placed the broken blade and bracer to one side, spread out the sheet, and, referring to it, began to rummage among a row of old books and manuscripts on a nearby shelf. Finding the two he wanted, he placed them on the table and began carefully to leaf through them.

‘What are you doing?’ asked Ezio, slightly impatiently.

‘This is very interesting,’ said Leonardo. ‘This looks very like a page from a Codex.’

‘A what?’

‘It’s a page from an ancient book. This isn’t printed, it’s in manuscript. It’s very old indeed. Have you any more of them?’

‘No.’

‘Pity. People shouldn’t tear the pages out of books like this.’ Leonardo paused. ‘Unless, perhaps, the whole thing together -‘

‘What?’

‘Nothing. Look, the contents of this page are encrypted; but if my theory is correct… based on these sketches it may very well be that…’

Ezio waited, but Leonardo was lost in a world of his own. He took a seat and waited patiently while Leonardo rummaged through and pored over a number of books and scrolls, making cross-references and notes, all in that curious left-handed mirror-writing he used. Ezio wasn’t the only one, he supposed, to live his life with one eye looking behind him. From the little he’d seen of what was going on in the studio, if the Church got wind of some of the things Leonardo was up to, he didn’t doubt that his friend would be for the high jump.

At last Leonardo looked up. But by that time Ezio was beginning to doze. ‘Remarkable,’ muttered Leonardo to himself, and then in a louder voice, ‘Remarkable! If we transpose the letters and then select every third…’

He set to work, drawing the blade, bracer and mechanism towards him. He dug out a toolbox from under the table, set up a vice, and quietly became absorbed in his work. An hour passed, two… Ezio by now was sleeping peacefully, lulled by the warm fug of the room and the gentle sounds of tapping and scraping as Leonardo worked on. And at last –

‘Ezio! Wake up!’

‘Eh?’

‘Look!’ And Leonardo pointed to the tabletop. The dagger blade, fully restored, had been fitted into the strange mechanism, which in turn was fixed to the bracer. Everything was polished and looked as if it had just been made, but nothing shone. ‘A matt finish, I decided,’ said Leonardo. ‘Like Roman armour. Anything which shines glints in the sun, and that’s a dead giveaway.’

Ezio picked up the weapon and hefted it in his hands. It was light, but the strong blade was perfectly balanced on it. Ezio had never seen anything like it. A spring-loaded dagger that he could conceal above his wrist. All he had to do was flex his hand and the blade would spring out, ready to slash or stab as its user desired.

‘I thought you were a man of peace,’ said Ezio, remembering the birds.

‘Ideas take precedence,’ said Leonardo with decision. ‘Whatever they are. Now,’ he added, producing a hammer and chisel from his toolbox. ‘You’re right-handed, aren’t you? Good. Then kindly place your right ring finger on this block.’

‘What are you doing?’

‘I’m sorry, but this is how it must be done. The blade is designed to ensure the total commitment of whoever wields it.’

‘What do you mean?’

‘It’ll only work if we have that finger off.’

Ezio blinked. His mind flashed on a number of images: he remembered Alberti’s supposed friendliness to his father, how Alberti had later reassured him after his father’s arrest, the executions, his own pursuit. He clamped his jaw. ‘Do it.’

‘Maybe I should use a cleaver. Cleaner cut that way.’ Leonardo produced one from a drawer in the table. ‘Now – just place your finger – così.’

Ezio steeled himself as Leonardo raised the cleaver. He closed his eyes as he heard it brought down – schunk! – into the wood of the block. But he’d felt no pain. He opened his eyes. The cleaver was stuck in the block, inches from his hand, which was intact.

‘You bastard!’ Ezio was shocked, and furious at this tasteless practical joke.

Leonardo raised his hands. ‘Calm yourself! It was just a bit of fun! Cruel, I admit, but I simply couldn’t resist. I wanted to see how determined you were. You see, the use of this machine originally did require such a sacrifice. Something to do with an ancient initiation ceremony, I think. But I’ve made one or two adjustments. So you can keep your finger. Look! The blade comes out well clear of them, and I’ve added a hilt that flips out when the blade’s extended. All you have to do is remember to keep them splayed as it’s coming out! So you can keep your finger. But you might like to wear gloves when you use it – the blade is keen.’

Ezio was too fascinated – and grateful – to be angry for long. ‘This is extraordinary,’ he said, opening and closing the dagger several times until he could time its use perfectly. ‘Incredible.’

‘Isn’t it?’ agreed Leonardo. ‘Are you sure you don’t have any more pages like this one?’