‘Yes,’ Clavain said, uneasily.
The rover itself ran on six wheels, a squat, pressurised hull perched low between absurd-looking balloon tyres. Galiana gunned them hard down the ramp and across the ice, trusting the machine to glide harmlessly over the smaller crevasses. It seemed reckless, but if they followed the trail Iverson had left, they were almost guaranteed not to hit any fatal obstacles.
‘Did you get anywhere with the source of the sickness?’ Clavain asked.
‘No breakthroughs yet—’
‘Then here’s a suggestion. Can you read my visual memory accurately?’ Clavain did not need an answer. ‘While you were finding Iverson’s body, I was looking over the lab samples. There were a lot of terrestrial organisms there. Could one of those have been responsible?’
‘You’d better replay the memory.’
Clavain did so: picturing himself looking over the rows of culture dishes, test tubes and gel slides; concentrating especially on those that had come from Earth rather than the locally obtained samples. In his mind’s eye the sample names refused to snap into clarity, but the machines Galiana had seeded through his head would already be locating the eidetically stored short-term memories and retrieving them with a clarity beyond the capabilities of Clavain’s own brain.
‘Now see if there’s anything there that might do the job.’
‘A terrestrial organism?’ Galiana sounded surprised. ‘Well, there might be something there, but I can’t see how it could have spread beyond the laboratory unless someone wanted it to.’
‘I think that’s exactly what happened.’
‘Sabotage?’
‘Yes.’
‘Well, we’ll know sooner or later. I’ve passed the information to the others. They’ll get back to me if they find a candidate. But I still don’t see why anyone would sabotage the entire base, even if it was possible. Overthrowing the von Neumann machines is one thing… mass suicide is another.’
‘I don’t think it was mass suicide. Mass murder, maybe.’
‘And Iverson’s your main suspect?’
‘He survived, didn’t he? And Setterholm scrawled a message in the ice just before he died. It must have been a warning about him.’ But even as he spoke, he knew there was a second possibility; one that he could not quite focus on.
Galiana swerved the rover to avoid a particularly deep and yawning chasm, shaded with vivid veins of turquoise blue.
‘There’s a small matter of missing motive.’
Clavain looked ahead, wondering if the thing he saw glinting in the distance was a trick of the eye. ‘I’m working on that,’ he said.
Galiana halted them next to the other rover. The two machines were parked at the lip of a slope-sided depression in the ice. It was not really steep enough to call a crevasse, although it was at least thirty or forty metres deep. From the rover’s cab it was not possible to see all the way into the powdery blue depths, although Clavain could certainly make out the fresh footprints descending into them. Up on the surface, marks like that would have been scoured away by the wind in days or hours, so these prints were very fresh. There were, he observed, two sets — someone heavy and confident and someone lighter, less sure of their footing.
Before they had taken the rover they had made sure there were two suits aboard it. They struggled into them, fiddling with the latches.
‘If I’m right,’ Clavain said, ‘this kind of precaution isn’t really necessary. Not for avoiding the sickness, anyway. But better safe than sorry.’
‘Excellent timing,’ Galiana said, snapping down her helmet and giving it a quarter twist to lock into place. ‘They’ve just pulled something from your memory, Nevil. There’s a family of single-celled organisms called dinoflagellates, one of which was present in the lab where we found Iverson. Something called Pfiesteria piscicida. Normally it’s an ambush predator that attacks fish.’
‘Could it have been responsible for the madness?’
‘It’s at least a strong contender. It has a taste for mammalian tissue as well. If it gets into the human nervous system it produces memory loss, disorientation — as well as a host of physical effects. It could have been dispersed as a toxic aerosol, released into the base’s air system. Someone with access to the lab’s facilities could have turned it from something merely nasty into something deadly, I think.’
‘We should have pinpointed it, Galiana. Didn’t we swab the air ducts?’
‘Yes, but we weren’t looking for something terrestrial. In fact we were excluding terrestrial organisms, only filtering for the basic biochemical building blocks of Diadem life. We just weren’t thinking in criminal terms.’
‘More fool us,’ Clavain said.
Suited now, they stepped outside. Clavain began to regret his haste in leaving the base so quickly; at having to make do with these old suits and lacking any means of defence. Wanting something in his hand for moral support, he examined the equipment stowed around the outside of the rover until he found an ice pick. It would not be much of a weapon, but he felt better for it.
‘You won’t need that,’ Galiana said.
‘What if Iverson turns nasty?’
‘You still won’t need it.’
But he kept hold of it anyway — an ice pick was an ice pick, after all — and the two of them walked to the point where the icy ground began to curve over the lip of the depression. Clavain examined the wrist of his suit, studying the cryptic and old-fashioned matrix of keypads that controlled the suit’s functions. On a whim he pressed something promising and was gratified when he felt crampons spike from the soles of his boots, anchoring him to the ice.
‘Iverson!’ he shouted. ‘Felka!’
But sound carried poorly beyond his helmet, and the ceaseless, whipping wind would have snatched his words away from the crevasse. There was nothing for it but to make the difficult trek into the blue depths. He led the way, his heart pounding in his chest, the old suit awkward and top-heavy. He almost lost his footing once or twice, and had to stop to catch his breath when he reached the level bottom of the depression, sweat running into his eyes.
He looked around. The footprints led horizontally for ten or fifteen metres, weaving between fragile, curtain-like formations of opal ice. On some clinical level he acknowledged that the place had a sinister charm — he imagined the wind breathing through those curtains of ice, making ethereal music — but the need to find Felka eclipsed such considerations. He focused only on the low, dark-blue hole of a tunnel in the ice ahead of them. The footprints vanished into the tunnel.
‘If the bastard’s taken her…’ Clavain said, tightening his grip on the pick. He switched on his helmet light and stooped into the tunnel, Galiana behind him. It was hard going; the tunnel wriggled, rose and descended for many tens of metres, and Clavain was unable to decide whether it was some weird natural feature — carved, perhaps, by a hot sub-glacial river — or whether it had been dug by hand, much more recently. The walls were veined with worm tracks: a marbling like an immense magnification of the human retina. Here and there Clavain saw the dark smudges of worms moving through cracks that were very close to the surface, though he knew it would be necessary to stare at them for long seconds before any movement was discernible. He groaned, the stooping becoming painful, and then the tunnel widened out dramatically. He realised that he had emerged into a much larger space.
It was still underground, although the ceiling glowed with the blue translucence of filtered daylight. The covering of ice could not have been more than a metre or two thick; a thin shell stretched like a dome over tens of metres of yawing nothing. Nearly sheer walls of delicately patterned ice rose up from a level, footprint-dappled floor.