Rivulets of nanomachines ran down the little hatch door, eating deeper and deeper into the metal surface, leaving a fine dust that drifted to the floor. Once they’d eaten away enough to leave a lip, the dust began piling up along the lower edge, so Ludokrus took a piece of paper from his pocket, folded it in a V, then carefully brushed the powder into it.
‘What are you doing?’ Coral said.
‘Saving the raw material. Maybe we can use.’
‘Raw material?’ She laughed. ‘We’re in a mine. We’re surrounded by raw materials.’
‘Yeah, but much rock must be refine to get at them. And to refine, the nanomachine will need the light. Our battery will not last so long.’ He stooped, made a neat pile of what he’d collected, and went back to gather more.
‘Almost there.’
He picked a large chunk of loosened metal free to reveal a square cut-out set into the wall.
‘Hah!’ Norman said. ‘Look, there’s the flashing light. The speaker too.’
‘Also microphone and camera.’
‘Camera?’ Coral said. ‘D’you mean they’ve been watching us?’
‘Not likely, the hatch was closed.’
‘Well, make sure they don’t.’
‘Easy.’ Ludokrus grabbed the camera and wrenched on it. Something snapped and it came free. He did the same with the other items, adding them to the recycling pile.
‘Right.’ Norman dusted off his hands. ‘That hatch is the sort of thing we’re looking for, just on a larger scale. Big enough for Tim and Alkemy to get through.’
* * *
Tim continued to retreat, the Sentinel continued to advance, stabbing its pointed antennae like a pair of spears and chittering a series of menacing screeches. He tried to force his way past, moving one way then darting back the other, but the Sentinel was too quick and stuck him in the side several times. Pin pricks, certainly, but still painful. Even if he could avoid the stabbing points, he’d still have to get past the creature’s bulk. It could easily squash and suffocate him against the tunnel wall.
Alkemy’s screams faded — that was one small mercy — but his feelings of helplessness and rage continued. He was furious at himself for not recognising the name of the gully, for not insisting on more caution, for not making some sort of weapon. But most of all he was furious at what these monsters were doing to his friend.
He stumbled backwards and found himself in the broad, cathedral-like fissure with its ribbon of light high above. Here he could get past the Sentinel, he thought. If it kept following him, he could simply step out of the etched channel and run past it. But the Sentinel spotted that weakness too and stopped, blocking the mouth of the tunnel and expanding to fill it completely like an enormous slimy plug.
Tim tried jeers and feints, tried running towards it then backing away, but apart from steadily tracking his movements with the pointed antennae, the Sentinel showed no reaction.
He was desperate now. The memory of Alkemy’s screams burned into his brain. He considered a reckless, suicidal charge. But it was hopeless. He’d be stabbed a hundred times even before he reached the Sentinel itself.
He turned in fury to the fissure, seeking something, anything, to throw, and spotted the crumbly crystals by the kink in the channel. Seizing one of the larger lumps, he rushed back and hurled it at the Sentinel.
It didn’t bounce or shatter, but struck the creature’s upper edge, passing into the gelatinous membrane and causing the tissue to pucker on its passage through. The frequency of the menacing chitters went up a notch and he realised he’d hurt it. He rushed back and gathered more.
‘Come on! Come on, what are you going to do about it?’ he yelled, holding up another piece of rock.
The Sentinel suddenly seemed wary. It flattened the pointed tip of one of antenna, transforming it into a paddle that it used to deflect the second rock.
Tim threw two more in quick succession. The first was knocked aside, but the second struck the paddle squarely and shattered. Fragments of the backscatter pierced the Sentinel and caused tiny puckers in its flesh.
‘Ha! Don’t like that, eh?’ Tim called. ‘Ready for another? Come on. Batter up!’
This time he hurled it deliberately high. The Sentinel tracked it for a second, saw it would miss then dropped its paddle, expecting a second, lower one. None came. The rock shattered on the wall above the passage, releasing a rain of small fragments. The Sentinel gave an alarmed chirrup and backed up.
Tim paused. The reaction seemed out of all proportion. The rock hadn’t hit it directly, yet small fragments seemed to do more damage than a large rock. Most curious of all was the way the Sentinel’s frilly underside reacted to the pieces that had fallen in the water, shrivelling and seeming to turn inside out.
Tim looked back at the whitish-yellow crystals and suddenly realised what they were. Rock salt. Just like terrestrial slugs and snails, the Sentinels couldn’t stand it. That’s why they’d cut the channel around the outcrop. To avoid the stuff entirely!
He stuffed as much as he could into the pockets of his jacket, then made a pouch from the front of his T-shirt and scooped more into that. He hurried back, scattering handfuls ahead of him like a farmer sowing seeds. The Sentinel puckered and edged away, deflecting what it could while shrinking from the tunnel walls and elongating itself to reduce its area of exposure. It started moving backwards, but slowly, and would no doubt recapture lost ground as soon as Tim went back to replenish his supplies. He’d need a mountain of rock salt to make any real progress.
The smaller stuff was running low, so he took out a large lump intending to break to it up. Then he had an idea. Instead of pounding it against the wall, he dropped it into the channel, ground it under his heel and sloshed the water forward with his foot. The reaction was immediate. The creature chittered shrilly and flailed furiously away, leaving long slimy tendrils in the salty water behind it.
Tim pursued it, but the Sentinel was in full retreat and moving fast. He had to run to keep up with it. All pretence at defence had vanished. The antennae disappeared as the creature focussed solely on escape. Now and then, at particularly tight curves in the passage, Tim was able to add to its distress by peppering its unprotected rear with handfuls of dust.
They passed the Y-junction, the passage straightened, and suddenly Tim knew where he was. There was alarm and confusion ahead as the second Sentinel fought to overtake the first, and the pair of them struggled to ooze back through the iron bars at the far end. Tim gave them an incentive, dumping the last of his hoard, grinding it up and sloshing it ahead.
Their high-pitched screeches faded as they fled. Silence returned. The agitated water in the bottom of the tunnel stilled and Tim moved on towards the darker section, bracing himself for what he would find there.