‘They are storming the city. To keep them at bay I must fire the cannon at targets within its walls.’

She looked at him with steely calm. ‘Then do what you must do.’

He looked up to the ramparts where Machiavelli stood, waiting for the signal. Ezio raised his arm, and lowered it decisively.

The cannon roared, and even as they did so Ezio was flying back up to the ramparts where they were located. Directing the gunners to fire at will, he watched as first one siege-engine and then another was blown to bits, as well as the catapults. There was little room for the Orsi troops to manoeuvre in the narrow streets and after the cannon had wreaked their havoc, Sforza archers and crossbowmen began to pick off the surviving invaders within the city walls. At last, the remaining Orsi troops had been driven out of Forlì altogether, and those Sforza troops who had survived outside the citadel itself were able to secure the outer curtain walls. But the victory had come at a cost. Several houses within the city were smouldering ruins, and in order to win it back, Caterina’s gunners had not been able to avoid killing some of their own people. And there was something else to consider, as Machiavelli was quick to point out. They had flushed the enemy out of the city, but they had not raised the siege. Forlì was still surrounded by Orsi battalions, cut off from supplies of fresh food and water; and Caterina’s two older children were still out there somewhere, at risk.

Some little time later, Caterina, Machiavelli and Ezio were standing on the ramparts of the outer walls surveying the host encamped around them. Behind them, the citizens of Forlì were doing their best to put the city back in order, but food and water wouldn’t last for ever and everyone knew it. Caterina was haggard, worried to death about her missing children – Bianca, the older, was nine, and Ottaviano a year younger.

They had yet to encounter the Orsi brothers themselves, but that very day a herald appeared at the centre of the enemy army and blew a clarion call. The troops parted like the sea to allow two men riding chestnut horses and dressed in chain-steel hauberks to pass between them, accompanied by pages bearing the crest of the bear-and-bush. They reined in well out of arrow range.

One of the horsemen stood up in his strirrups and raised his voice. ‘Caterina! Caterina Sforza! We think you are still cooped up in your dear little city, Caterina – so answer me!’

Caterina leant over the battlements, a wild expression on her face. ‘What do you want?’

The man grinned broadly. ‘Oh, nothing. I was just wondering if you were missing… any children!’

Ezio had taken up a position at Caterina’s side. The man who was speaking looked up at him in surprise. ‘Well, well,’ he said. ‘Ezio Auditore, if I am not mistaken. How pleasant to meet you. One has heard so much about you.’

‘And you, I take it, are the fratelli Orsi,’ Ezio said.

The one who had not yet spoken raised a hand. ‘The same. Lodovico -‘

‘- and Checco,’ said the other. ‘At your service!’ He gave a dry laugh.

‘Basta!‘ cried Caterina. ‘Enough of this! Where are my children? Let them go!’

Lodovico bowed ironically in the saddle. ‘Ma certo, Signora. We’ll happily give them back. In exchange for something of yours. Something, rather, that belonged to your late lamented husband. Something he was working on, on behalf of… some friends of ours.’ His voice suddenly hardened. ‘I mean a certain Map!’

‘And a certain Apple, too,’ added Checco. ‘Oh yes, we know all about that. Do you think we are fools? Do you think our employer doesn’t have spies?’

‘Yes,’ said Lodovico. ‘We’ll have the Apple too. Or shall I slice your little ones’ throats from ear to ear and send them to join their pappa?’

Caterina stood listening. Her mood had changed to one of icy calm. When her turn came to speak, she cried, ‘Bastardi! You think you can intimidate me with your vulgar threats? You scum! I’ll give you nothing! You want my children? Take them! I have the means to make more!’ And she raised her skirts to show them her vagina.

‘I’m not interested in your histrionics, Caterina,’ said Checco, wheeling his horse around. ‘And I’m not interested in staring at your figa either. You’ll change your mind, but we’re only giving you an hour. Your brats will be safe enough until then in that slummy little village of yours just down the road. And don’t forget – we will kill them and then we will come back and smash your city and take what we want by force – so you just take advantage of our generosity and we can all save ourselves a lot of bother.’

And the brothers rode off. Caterina collapsed against the rough wall of the rampart, breathing heavily through her mouth, in shock at what she’d just said and done.

Ezio was by her side. ‘You’re not going to sacrifice your children, Caterina. No Cause could ever be worth that.’

‘To save the world?’ She looked at him, lips parted, pale blue eyes wide under her mane of red hair.

‘We cannot become people like them,’ said Ezio simply. ‘There are some compromises which cannot be made.’

‘Oh, Ezio! That is what I expected you to say!’ She flung her arms round his neck. ‘Of course we can’t sacrifice them, my darling!’ She stood back. ‘But I cannot ask you to take the risk of getting them back for me.’

‘Try me,’ said Ezio. He turned to Machiavelli. ‘I won’t be gone long – I hope. But whatever happens to me, I know you will guard the Apple with your life. And Caterina -‘

‘Yes?’

‘Do you know where Girolamo hid the Map?’

‘I’ll find it.’

‘Do so, and protect it.’

‘And what will you do about the Orsi?’ asked Machiavelli.

‘They are already added to my list,’ said Ezio. ‘They belong to the company of men who killed my kinsmen and destroyed my family. But I now see that there is a greater Cause to be served than mere revenge.’ The two men shook hands and their eyes locked.

‘Buona fortuna, amico mio,’ said Machiavelli sternly.

‘Buona fortuna anche.’

It wasn’t hard to reach the village whose identity Checco had so carelessly given away, even if his description of it as a slum had been a little ungracious. It was small and poor, like most serf-villages in the Romagna, and it showed signs of having recently been flooded by its nearby river; but on the whole it was neat and clean, the houses roughly whitewashed and the thatch new. Although the water-logged road that divided the dozen or so houses was still mired from the flood, everything suggested order, if not contentment, and industry, if not happiness. The only thing which distinguished Santa Salvaza from a peacetime village was that it was peppered with Orsi men-at-arms. No wonder, mused Ezio, that Checco thought he could afford to mention where he was holding Bianca and Ottaviano. The next question was, where exactly in the village might Caterina’s children be located?