Master Able had always maintained that unless and until it could be proven that the visitors were something other than phantoms or delusions, any attempt to speculate about their nature and motives would be no more than an amusing but futile intellectual game, for theories that lacked a firm foundation of fact were no better than the fantasies spun by self-important pseudo-scholars like Intrepid Windrush. But as he studied the ruins Pilgrim couldn’t help hoping that Mercy’s account was real and true, couldn’t help wondering why the visitors had come here and what they might have been trawling for with their nets of ghost light.

He asked Mercy where he had taken refuge, and the scout pointed to a spot a little way down the track that descended towards the ruins, said that he’d crawled under a clump of thorn bushes and hadn’t moved until the lights went out and the white flame shot up.

‘You had a good view.’

‘Ay-ya. Even with the fog.’

‘We should show our guest that patch of burnt ground, cousin,’ Righteous said.

The trotcart rattled down the track, cut around blocks of stone that littered the space between the brooding hulks of two pyramids. A thin scrub of dry grass and dwarf juniper had colonised their tiers, overtopped by tall risers decorated with carved panels and pierced with the square mouths of shafts that piped sunlight to the chambers inside. Righteous pointed out a long scar on one riser where panels had been prised away by scavengers, saying that scenes of battle and the like seemed to be the most popular prizes.

The track gave out at a square filled edge to edge with thorn bushes, and the sepulchral silence of the ruins was briefly broken when a flock of small green birds whirled up, screeching indignantly at the trotcart and each other before fleeing around the flank of one of the pyramids. Pilgrim, Righteous and Mercy climbed down from the trotcart and followed a narrow path tunnelled through the thorns to the narrow point of the city’s prow, where a lone pyramid stood against the hot blank sky.

The scar left by the white flame was in the shadow of the pyramid’s footing. It was much bigger than Pilgrim had expected, an oval of charcoal and ash ten ells across at its widest point, perhaps twice that in length. He took out his dip pen and bottle of ink, turned through his jotter to one of the pages of smooth vellum he’d had bound in the back and made a quick sketch, telling Mercy and Righteous that two other witnesses had mentioned seeing something fly off into the sky after their encounters with the visitors.

‘One said it was shaped something like the pip of a sourapple; the other described a blunt cylinder, and found a burnt patch much like this.’

‘I didn’t see anything but the fire,’ Mercy said.