With ringing ears and numb fingers I located the view-ring amid the sparkling rubble and hastened through the doorway. A corridor led straight ahead, appearing to divide the ground floor. At the far end I glimpsed steps – presumably the stair that wound around just inside the tower walls. Half a dozen young Liban men in white tunics headed toward me from arches to either side of the corridor, their looks those of scholars, astonishment rather than anger on their faces. I drew my knife and let the sleeve of my robes fall around it. Looks can be deceiving.

‘Something’s wrong with your door.’ Without pause I strode between them.

On reaching the stairs, which led off down and up, I chose up. I retied the view-ring on its thong, fumbling the knots, fingers still buzzing.

I had it from Omal that the mathema was more by way of a university, a place of study for the mathmagicians. Qalasadi was some sort of teacher. A tutor to the caliph’s children, a guide for students come to study at Hamada, an arbiter in the affairs of lesser lights amongst the numbered men, as they liked to call themselves. The tower was not his home, not his domain or fiefdom, but even so, somehow I thought I might find him at the top.

Equations kept pace with me as I walked the worn steps, climbing the mathema tower knife in hand. Some ran the full length of the spiral stair, others started and ended within a few yards to be replaced by fresh calculations, all carved into the stonework then inlaid with black wax to make them legible. I passed door after door, each set with a letter from the Greek, starting with ‘alpha’, next ‘beta’. By ‘mu’ I had reached the first of the windows and a cooling breeze spiralled up with me. I passed two mathmagicians coming down, both old men, wrinkled like prunes and so deep in conversation I could have been on fire and gone unremarked.

And finally, where the last window offered Hamada in a broad, bright panorama, the steps ended at a door set with ‘omega’, inlaid in brass into the mahogany. I gave myself a moment. I’d rather climb mountains than steps.

I let my sleeve hide the blade once more and pushed the door. It swung open with a soft complaint of hinges and there, leaning over a wide and glossy desk at the centre of a single circular room, Qalasadi, Yusuf, and Kalal. They looked up in unison and the moment of surprise written on those three faces proved all the reward I could want for my long climb. Yusuf and Kalal immediately bent their head back to the papers as if hunting for an error amidst their scratchings. Both men clutched quills, their fingers stained as black as their teeth.

‘Jorg.’ Qalasadi recovered his composure in the space between two breaths. ‘Our projections indicated the front door would take you considerably longer to pass.’

Yusuf and Kalal exchanged glances, as if asking what other errors may have crept into their calculations.

‘Your projections? For men who want to put out the Builders’ eyes you surely sound a lot like them.’

Qalasadi spread his hands, empty, ink-stained. ‘It’s our actions that define us, not the manner in which we reach the decision to act.’

I threw the dagger, moving my arm across my body so the action would not be telegraphed. The blade bedded in the gleaming table, hilt quivering, a hand’s breadth from Qalasadi’s groin. I’d been aiming for roughly that spot but it was a tricky throw, a flat angle and an awkward motion. I’d thought it a reasonable chance the knife would glance off and end up in his scrotum.

‘Is that on your papers? Had you figured that one out?’ I strode toward the table. ‘Did you have the knife’s trajectory plotted?’

Qalasadi put a hand on Yusuf’s shoulder. The younger men ceased their scribbling and looked up, still hung with frowns as if more concerned by their calculus than my sharp edges.

‘Can I get you a drink, King Jorg?’ Qalasadi said. ‘It’s a long climb up all those steps.’ The ivory wand he’d used to write in the dust of my grandfather’s courtyard lay in his hand now.

I came to the table, just its width between us, my knife skewering a sheath of papers, all covered with tight-packed symbology, and spoke in a calm voice, as reasonable men do. ‘Part of being in the business of prediction, a large part perhaps, must be the art of giving the impression that things are unfolding according to your expectations. A victim who believes himself anticipated at every turn is not only crippled by uncertainty but also easier to predict.’

All three men watched me without reply. No sign of nerves, save perhaps Qalasadi’s fingers rubbing at the short curls of his beard, and a faint sheen of sweat across Kalal’s brow. Yusuf had taken the combs from his hair and bound it all back, tight to the skull. He looked older now, more clever.

‘You must have known I would decide to hit the table with that throw or you would have tried to stop me … unless you didn’t know I would throw the knife at all?’ I found myself digging into the crippling uncertainty I’d just spoken of.

‘And the drink?’ Qalasadi said.

I did have a thirst on me, but that was too predictable. Besides, you don’t cross nations to hunt down a poisoner and then drink what he gives you. ‘Why did you try to kill my mother’s kin, Qalasadi? A friend told me the mathmagicians have their own purposes. Was it just to please Ibn Fayed? To keep his good will and stop him turfing you out of this rather fine oasis?’

Qalasadi rubbed his chin across the top of his palm, closing his fingers about his jaw in consideration. He had the same even pace to him that he showed in Castle Morrow. I had liked him from the start. Perhaps that’s why I showed off for him, maybe gave him the information he needed to deduce my story. Even now, with vengeance a sword thrust away, I had no hatred for him.

‘It’s an irony of our times that men seeking peace must make war,’ he said. ‘You know it yourself, Jorg. The Hundred War must be won if it is to stop. Won on the battlefield, won on the floor of Congression. These things are of a piece.’

‘And Ibn Fayed is the man to win it?’ I asked.

‘In five years Ibn Fayed will vote for Orrin of Arrow at Congression. The Earl Hansa would not. The vote will be close. The Prince of Arrow will bring peace. Millions will prosper. Hundreds of thousands will live instead of dying in war. Our order chose the many over the few.’

‘That was a mistake. They were my few.’ A heat rose in me.

‘Mistakes can be made.’ He nodded, thoughtful. ‘Even with enchantment to tame the variables the sum of the world is a complex one.’

‘So you still intend to gift the realm of Morrow to Ibn Fayed? To let the Moorish tide back yet again into the Horse Coast?’ I watched Qalasadi, his eyes, his mouth, the motion of his hands, everything, just to try and read something of the man. It maddened me to have them stand there so calm, as if they knew at each moment what was on my tongue to speak, in my mind to do. And yet did they? Was it part of their show of smokes and mirrors?

‘We intend that the Prince of Arrow win the empire throne at Congression in the 104th year of Interregnum.’ Yusuf spoke for the first time, his voice edged with just a touch of strain. ‘The Congression of year 100 will be a stalemate: that cannot be changed.’

‘It may be that the caliph’s domains can more easily be expanded in other directions.’ Kalal spoke, his high voice at odds with a serious mouth. ‘Maroc may fall more easily than Morrow or Kordoba.’