Chris felt as if he had been asleep for just seconds when Kate woke him urgently.
"What's the matter?" he groaned.
His rucksack had been a poor choice of pillow and had left him with a sore neck. He stretched his head to one side in an attempt to relieve the pain in his neck muscles.
"Wake up! I can hear something outside," she whispered sharply.
Chris rolled onto his back and struggled to sit up. The surrounding chamber was dark apart from two torches shining up onto the curved metal surface arching above them. As far as he could tell, everyone else was still asleep.
"What time is it?" he whispered.
"About two hours after we settled down," she replied. "But don't worry about that. There's something moving about out there!"
"I can't hear anything. Are you sure you weren't just dreaming?"
All Chris could hear was Fletcher snoring.
"No way. I've heard it seven or eight times since it woke..." she stopped as a metallic scraping sound resonated through the supply module's hull.
Chris, with an extra burst of energy, scrambled to his feet. "Okay, I heard that."
"See!" said Kate, getting to her feet too.
"Could it be the sound of the module settling, or components cooling down?"
"I think it sounds like something is trying to climb up the outside," she whispered, visibly shuddering at the thought.
"Even if there is something out there, it won't be able to get through the hull, plus the bottom two-thirds is filled with solid ice. There's no way it can get to us."
"But what the hell is it?" she asked.
They fell silent again as a dull tapping sound repeated erratically half-a-dozen times. A momentary pause followed, and then more tapping. Chris and Kate stared into each other's eyes, waiting for the next sound. Some thirty seconds later, there was a long scraping noise, then yet more tapping.
"That's not settling noises, is it?" she asked quietly.
"No, someone's definitely out there."
"If it was one of our crew, wouldn't they be calling for help?" she asked.
"I would think so. Why would..."
He fell quiet again when a clunk noise, apparently much closer, rang out. Moments later there was another identical clunk. They both realised that they were hearing heavy footfalls on the metal ladder tied to the side of the module. Chris suddenly wished they had pulled up the rope which dangled over the side to meet the ladder, but he never expected any reason to do so at the time.
More clanks, barely a second apart, followed. Someone or something was making use of the ladder. Chris tried to ignore his pounding heart and whirled into action. He padded across to Fletcher's sleeping form and jabbed his shoulder.
"Fletcher, wake up, quick!"
Fletcher grunted and pushed Chris away.
"Get up now, I need your help," he urged, shaking Fletcher's shoulder again.
Chris did not wait, but moved to stand directly below the hatch.
"What's going on, Commander?" Fletcher asked at full volume.
Chris shushed him then whispered, "We need to secure the hatch right now, but don't make any noise."
"Secure it? Why?!" Fletcher whispered back.
The various sounds woke Lucy, who immediately sat up in a panic before calming herself.
"There's no way to seal the hatch from the inside, Commander," said Fletcher, groaning as he clambered to his feet.
The clunks ended but, after a couple of bangs, a slow scraping sound took over. Whatever it was, it was clearly above them now and seemed to be heading for the hatch. Chris reached up to the hatch wheel but it was apparent that Fletcher was right; it was just a wheel with no way to stop it being opened from the outside.
The scraping paused, started again for a second, but heavy, plodding footsteps replaced it again. Instead of clanging, they thudded directly against the hull. Fletcher joined Chris by the hatch wheel, then they all listened in silence. Lucy began quietly waking Amanda and Anil.
"What's going on out there now?" Fletcher whispered.
"I don't know," Chris shook his head. "The wheel is recessed. Maybe it can't find it?"
"Is it Melissa? Did she follow us?" he asked.
"Melissa's not that heavy, it doesn't sound like it can be her, but I don't know."
The pause in noises ended with another heavy thud followed by a sudden movement in the hatch wheel. Chris's heart sank as both he and Fletcher reached up and grabbed the wheel. That was enough to stop it dead.
They looked at each other in silence, still gripping the wheel. It jerked again, this time overpowering them. Kate rushed across and stretched up to grab the wheel too. With it at full arm's reach for her, she could not apply much force.
"Anil! Lucy! Get over here and help!" she hissed quietly.
Lucy arrived first, followed by the others. Soon all six of them were holding onto the outside of the wheel, slowing it to a halt again. All straining to hold it as hard as they could while trying not to slip on the parachute fabric covered ice, they resisted several more jerks of the wheel. Between each jerk, they turned it tightly closed again.
"How long do we do this for?" asked Anil.
"As long as we need to," Fletcher shrugged. "Whatever's doing this is much stronger than any of us. We can't let it in here, lad."
The wheel kicked again, a half turn this time, throwing Kate off her feet and pulling everyone else around with it.
"Can you hold it for a mo, Commander?" Fletcher whispered sharply.
"Er... no!" Chris replied.
Fletcher ignored him, released the wheel and dived for the length of ladder they had used to get inside the module. It was lying near the right-hand side of the hull. He scooped it off the ice floor like it weighed nothing at all and rammed the top between the spokes of the wheel. After twisting it to jam the wheel, he jammed it down into the floor and lay up it, using his weight to anchor it in position.
Above them the wheel jerked again, jolting the ladder but failing to move it. Chris kept on gripping the wheel, but Lucy and Anil moved to the bottom half of the ladder, adding their weight to it and holding it from either side. The wheel jerked again, creaking the ladder, but they all clung on and the ladder held fast.
Chris tentatively released his grip on the wheel and looked at the others. It jerked powerfully several more times before whatever was trying to open it seemed to give up, for a while at least. The only problem with the ladder arrangement was that it also stopped them resealing the hatch, which Chris reckoned was somewhere around half unscrewed.
There was silence for a few moments. No-one dared to say anything, but everyone stared up at the hatch wheel, expecting it to jerk again at any moment. Instead, there was a gentle scraping sound followed by two more footfall-like thuds and then silence.
"What do we do now?" Lucy whispered.
"I think it's given up for now," Chris replied.
"But it's still up there," added Fletcher.
"And there's nothing stopping it trying again later on," said Kate.
"No sleep for us then," Lucy sighed.
"We should climb out, push it off the top of the module and pull up the rope to stop it getting up here again," Fletcher suggested.
"That would solve the problem," Chris replied. "But we could only get out of the module one at a time. Whatever is up there could take us out individually as we climb out. You felt how hard it turned that wheel."
"How do we know that thing won't just drop in here if we open the hatch?" asked Kate. "It's trying to get in here, regardless."
"We can't risk that," replied Chris. "It's a stalemate right now. Whatever it is, it can't get in and while it's there, we can't get out. The question is, will it keep trying, will it give up and leave or just sit up there and wait for us to come out?"
"How can we possibly know?" exclaimed Lucy.
"We can't," he shrugged. "All I know is that we're safe as long as we don't let it get in here."
"We're going to hide in here indefinitely?" asked Fletcher.
Chris stepped back from the hatch. "No, our food will run out and the heaters won't last forever. We can afford to stay here until morning. That was our original plan anyway."
"We just wait?" asked Kate.
"Five of us sleep. One stays on guard duty, then halfway through what's left of the night, someone else takes over as guard. If that wheel moves at all, whoever's on duty can raise the alarm. I'll take the first shift."
"No, you won't," Lucy replied. "While you're leading this team, you need to get your sleep. I'll take the first shift."