When they were a kilometre down, it became obvious they had reached the point where the probe had been destroyed. Pieces of wreckage were imbedded in the rock, and the ice was blackened by smoke. Beyond this point there were long score marks in the ice, and splinters of the glassy rock itself had been broken away.

‘Looks like the probe dislodged something,’ said Gant.

‘Some sort of grating—a barrier?’ Cormac wondered.

‘The probe would have halted at it,’ Carn said. ‘Anyway, no sign of any fixings.’

Cormac studied the gouges. They were almost like claw marks and he did not like the image this conjured up. It seemed that whatever had been dislodged had scrabbled frantically to maintain its position. It had failed, but left marks all round the shaft, which gave an indication of its size. Cormac began to have serious misgivings.

‘Stay sharp,’ he said, and noticed then that Cento and Gant had already drawn their weapons.

When they were still a half kilometre from the chamber, Cormac suddenly felt a strange beating under his breastbone. This rhythm increased in frequency till, with a thrill through his entire body, it exceeded the range where he could feel it. A darkness then occluded the lights below and there came a sound as of a ton of scrap iron being rolled across the ice and stone. A shape filled the shaft and started to draw closer. It looked like a cross between a trapdoor spider and a tick, but made of polished chrome. It was huge, a nightmare, and it was coming fast.

‘Jesus!’ yelled Gant.

‘Hit it!’ yelled Cormac. It seemed more than likely that it was not coming to welcome them.

Candent flashes filled the tunnel. Stone was blasted in molten droplets from the wall. Cormac saw one chrome leg drop away, then—as a growing cloud of CO2 vapour filled the shaft—the creature was on Gant and Cento.

‘Pull back!’

The line Carn was attached to, which led to Cento, whipped to one side and Carn fell against the wall of the shaft. In the vapour there were more flashes and a sound like a compressor starting up.

‘They’re bouncing off! Jesus! Cento!’ came Gant’s yell. He came backwards out of the cloud, firing as he came, stripped-off filament cladding falling round his feet. Then came the creature, scrabbling for a grip on the walls of the shaft. Many of its legs were now missing and there were scores along its teardrop body, but it had legs still to spare and did not seem to notice the damage. Its triclaw mandibles opened and snapped shut around Gant, even while he was firing into its mouth. He yelled and swore.