Moving rapidly to mask his own fear, Ibrahim walked the last few paces to the bridge, and stood boldly between the mob and its prey. He glanced at the victim, who was a slim man, breathing hard, his face so bloodied it was unrecognisable.

Then Ibrahim turned to face the mob. The crowd was perhaps fifty strong, mostly men, a few women. They were all as ragged and dirty as the man they hunted. Ibrahim knew these people. Without homes, without hope, they were profoundly afraid. But fear was easier to bear if you could find somebody to hate.

He spread his hands to show he was unarmed. Abdul was watching closely, his hand on his scimitar.

Ibrahim called, ‘Why are you here? Why do you keep me away from my prayers?’

There was an inchoate growl. One man waved a ragged bit of parchment in the air.

‘You.’ Ibrahim picked on the man and strode forward. ‘Come here!’

The man instinctively stepped forward, and the crowd pressed back. Suddenly the man looked less certain, for he was once again a man, himself, and not a component of the mob.

‘Tell me your name,’ snapped Ibrahim. ‘In me, you face the authority of the vizier. Tell me!’

‘I am Gabirol,’ he said reluctantly. He was probably no older than Ibrahim.

Ibrahim nodded. He turned to Abdul, who made a show of writing down the man’s name. ‘All right, Gabirol. My goal here is to secure the peace. That’s all I care about. We can’t have crowds running around with torches and knives, and we can’t have citizens torn apart on our streets—’

‘He’s no citizen,’ Gabirol snapped, and his anger surged. He waved his bit of parchment at the man on the bridge. ‘He’s a spy! A spy for Fernando, for the Christians.’

A city under threat was rife with rumours, riddled with imagined traitors and spies - and perhaps a few real ones. ‘And how do you know that?’

‘Because of this! This is what he was carrying when he was found.’ He held up the parchment again.

Ibrahim took it gingerly. Streaked with blood, it was covered with sketches of what looked like fish. Perhaps they were anatomical drawings. But when he looked more closely he saw that there were bits of machinery inside each ‘fish’, gears and levers and pulleys, and sketches of tiny men who pulled on oars or worked at capstans.

He growled, ‘Oh, Mother, what have you done?’

Abdul looked at him. ‘What was that, sir?’

‘Never mind. So, Gabirol, you think he’s a spy because of these sketches.’

‘Isn’t it obvious? Everybody knows Fernando wants to block up the river. Maybe this is the way he’s going to do it, with these fancy ships—’

‘It’s the shape that gives it away.’ A woman stepped forward now, her face twisted into a fearful rage.

‘What shape?’