Saladin and Thomas were not permitted to go with the scouting party to the foot of the walls beneath the strange explosion. But they were able to inspect what was recovered: some twisted bits of metal, and an immense ball of iron.

‘An engine,’ Thomas said darkly. ‘Or the remains of one that failed.’

‘Subh,’ Saladin said. ‘My mother’s cousin. She is in there. This proves it.’ He glanced at the city walls, and wondered if this remote relative whom he had never met was looking back at him now. ‘She must have the engine plans. She must have dug them up from the mosque-‘

‘Not necessarily. Fernando has the city riddled with his spies. If that were going on we’d have heard about it. Subh’s letter to your mother hinted of other designs, sketches developed by Sihtric and his co-workers from the originals – sketches that were not entirely lost when Sihtric died. Perhaps that’s what we’re seeing here.’ He grunted, poking tentatively at a bit of torn copper sheet. ‘It would certainly explain why it failed. We may yet not be too late to get to those originals first.’

‘I hope so. Or mother will be furious.’