Before long they reached the crossroads at the asteroid’s heart. Someone had directed a spider to nail up a handwritten sign indicating basic directions. Ty braked, and waited for Nancy to do the same.

‘We’re going into Chamber Two,’ he explained, nodding in the direction of Shaft B West. ‘It’s pressurized, okay? That means we can—’

‘Nathan, I know you’re dedicated to your work, but get your head out of your ass. Remember I’m the one who writes the daily progress reports. What makes you think I don’t already know it’s pressurized?’

‘Sorry I was just thinking out loud. Another hundred metres, then down the hatch.’

The Atn usually left a basic assortment of data and tools behind whenever they abandoned a clade-world, but in this case there seemed to be a surfeit of artefacts both physical and virtual. The data was recorded on storage devices built around a core of self-repairing molecular circuitry, the resulting stacks resembling rows of bronzed shields embedded in the walls of dedicated chambers. Most, but not all of the data stored there still remained incomprehensible to human researchers.

The stack chamber was accessed through a pressure seal installed by spider-mechs shortly after their arrival. They passed through the airlock quickly, Ty pulling off his helmet once they were inside the chamber. He watched as Nancy did the same, shaking sweat from frizzy blond hair cut into a bob.

The chamber was rectangular, its walls crowded with the ubiquitous spiral-form glyphs. A heap of what might appear to the casual observer as nothing more than blackened junk lay jumbled in one corner. The remains of eight Atn stack-discs were embedded in the wall directly opposite the pressure seal. Each had been carefully and deliberately vandalized; fragments and chunks of the discs lay scattered all around.

Nancy knelt by the pile of junk and poked at it with one gloved finger. ‘I don’t know, Nathan, we’ve already been over every inch of this place, and I’ll be seriously surprised if we’ve missed anything.’

Ty pulled off a glove and ran one hand over the ruined edge of a stack-disc. ‘We missed one thing.’ He nodded towards the pile of junk in the corner. ‘That’s the remains of an Atn, for a start.’

‘Oh.’ She stood up and took a step back. ‘Are you sure?’

He glanced past her at the twisted remains, which were hardly recognizable as having ever been anything living. ‘I ran a tomographic analysis on some trace organic remnants. It’s definitely the remains of an Atn, and it’s been subjected to extremely intense levels of heat, like something turned the interior of this chamber into a furnace. You remember what Cesar found out about those craters?’

A lot of them were formed relatively recently, and in the same short period of time, right?’

‘Exactly It’s like something turned up here, killed everything living it found, then disappeared again.’