Once he and the Doctor were safely on top of the precipice, Cameron dumped the bundle in front of his men and slumped against the junk metal, breathless.

“Where’s the captain?” said Private Doherty.

It was Private Wells who lifted up the lapel of Cameron’s jacket.

“Oh my god,” he breathed, dropping it again in shock.

One by one the men peered inside the discomposing package. Corporal Ryan looked last, and left the jacket flapped open so they could see Captain Hamilton’s dead-eyed stare. For almost a minute, nobody said anything.

“Why’d they put a damn robot in charge of our platoon?” said Private Cooper.

“And why didn’t they tell us?” said Wells.

“Maybe they didn’t know,” Private Spooner muttered.

“Yeah, Spooner's right; I mean, we couldn’t tell,” Doherty concurred.

“He looks so…real,” Private Ellison hissed.

Spooner sighed. “Maybe that’s the point.”

“If one robot’s infiltrated the military, then how many others have?!”

“What about a medical? They must have known.”

“Yeah; bio-scan this thing and you’d see it immediately.”

“You just called the captain a thing, Spoon!”

“Spooner’s right, though; he is a thing. He’s not one of us.”

“We took our orders from a machine; I can’t believe it.”

“It must be some sort of conspiracy.”

“But the captain hated droids; how could he be one?”

“That was all part of the subterfuge.”

“Yeah! What better a droid-killer than another droid?”

“Or perhaps he didn’t know himself,” said the Doctor.

They all turned to look at him.

Whilst the marines had been bartering theories and explanations, the Doctor had decided to take a closer look at one of the other corpses. He found one with a red cross on his helmet; he guessed this was the med-tech, Daniels.

Crouching down, the Doctor turned the body over. Daniels’s eyes were blank and unfocussed. The Doctor reached into his coat for the sonic screwdriver.

“Maybe they didn’t know,” someone said behind him.

The Doctor adjusted the sonic screwdriver to its lowest setting. The end glowed blue, but the hum it emitted was practically inaudible.

Glancing out of the corner of his eyes to make sure he wasn’t being watched, the Doctor waved the sonic screwdriver across Daniels’s face like a torch.

Daniels’s eyes followed like iron to magnets.

“He’s not one of us,” someone was saying behind the Doctor.

The Doctor stood up and turned toward them.

“What do you mean, Doctor?” Sergeant Cameron said.

“How could he not know?” Corporal Ryan sneered.

The Doctor took a deep breath. “It was like I was telling Rose, about the first Universal Definition and Protection of Sentience Act of 2181, before the Io Accord; how Eve-series droids were deliberately programmed not to be self-aware. This is just a variation on a theme of that: Captain Hamilton was self-aware of his individuality, of his rights as a person; he just wasn’t self-aware of the fact that he wasn’t a person at all. Not a human one, in the strictest sense of the word, at any least.”

Cameron laughed. “That’s crazy; that’s impossible!”

“I think Mr Daniels would disagree there.”

“What’s that supposed to mean?”

The Doctor invited them to take a look. As they stood over Private Daniels’s crumpled corpse, the Doctor took out his contraption; the thing he’d used to bring down the first droid that had attacked them, and waved it over Daniels’s face.

The med-tech’s eyes swivelled in their sockets.

Cameron started. “Jesus!”

“He’s still alive!” Private Wells cried.

“No, he’s not,” said the Doctor, feeling Daniels’s limp arm for a pulse. “But strictly speaking, he never was, anyway.”

“But his eyes moved!”

The Doctor held his metal device up like a candle. “That was me; and this thing doesn’t work on humans, I’m afraid.”

For a moment, they were all too shocked to speak.

“Daniels is a robot?” Wells said under his breath; his tone would have been hysterical had he been saying it any louder. “Daniels is a robot?”

“This isn’t happening.” Ryan shook his head.

“What the hell’s going on, Sarge?” Private Cooper hissed.

“But he can’t be a robot!” Wells cried. “I’ve known him since sixth grade!”

The Doctor stood up. “Really?” he said absently.

“We went to high school together,” Wells went on. “I’ve been to every one of his birthday parties since he was thirteen, except for his sixteenth; because we fell out after I said his sister was hot. The first time I got drunk - was with him. The first time I smoked a joint - was with him. The first time I got laid - was at his seventeenth birthday party, with his sister. His sister! Robots don’t have sisters!”

“Well, I can perform a more thorough forensic examination if that’s what it’ll take to convince you,” the Doctor said with a sigh.

Cameron put a hand on his arm. “That won’t be necessary.”

“I’ve got it!” Wells hissed. “He’s been replaced! This isn’t the real Daniels; this is a perfect robotic replica, designed to look like him, sound like him, act like him, and convince us that it is him, but it isn’t him. What better way for the Syndicate to infiltrate our ranks than replace the captain and Daniels with replicas? It makes sense, Sarge; one of them could have sabotaged the shuttle!”

Cameron looked at Daniels and frowned. Daniels had been in his squad for three years and he’d never noticed a change. Same with Captain Hamilton; Cameron had served under him for almost five. Had robotic science really come so far as to enable absolutely perfect, indistinguishable replicas of humans to be built?

Their mutterings implied his men certainly thought so.

“Entia non sunt multiplicanda praeter necessitatem,” said the Doctor.

The men stopped muttering and looked at him.

“What did you just say?” Cameron said.

“Are you familiar with the principle of Occam’s Razor, Sergeant?”

The sergeant frowned. “No; what is it, Doctor?”

“It’s a philosophical concept,” the Doctor went on. “One of the most basic, concise statements of reason in the entire school of rationalist thought. It’s expressed in Latin as: Entia non sunt multiplicanda praeter necessitatem; roughly translated that works out as: no more things should be presumed to exist than are absolutely necessary. In essence, the simplest answer is also the likeliest one.”

“And what’s the simplest answer, Doctor?”

“That Daniels and Captain Hamilton were always robots.”

Most of the men reacted badly to hearing this:

“Rubbish; that’s impossible!” said Ryan.

“You don’t know what you’re talking about!” went Cooper.

The Doctor sighed. “I said it was the simplest answer; not the most popular.”

“But I remember him as a kid,” Wells said.

Cameron turned to look at him. The private wasn’t deriding the Doctor like the others. He was staring at Daniels’s body, frowning pensively.

“But if he’s a robot, then he never was a kid, was he?” Wells went on. “So why do I remember it? Why do I remember it like it was only this morning?”

He looked up at Sergeant Cameron slowly.

“If he’s not real; and my memories aren’t real…”

He trailed off. Nobody had an answer, but Cameron glanced at the Doctor and with his return look came a sudden, horrifying realisation.

But he reckoned Wells had just arrived at the same place too.

“What the hell are you doing, Wells?” Ryan cried as Wells bent down, unsheathed his combat knife and sliced a four inch gash along his own forearm.

Cameron wasn’t surprised when no blood eked out.

“Oh my god,” Wells said under his breath.

With his thumb and middle finger, he parted the wound. The gap between was wide enough to stick his forefinger in and clear the sticky black fluid.

Where there should have been bone, there was metal.

“Oh my god,” Wells said again.

It was a sentiment echoed by his comrades; then they were silent for perhaps half a minute. Eventually, Private Spooner chuckled nervously.

“Well, I know what I am, but you guys have made me paranoid now.”

Then he drew his own knife and cut himself too.

He cut too deep. He severed some mechanism in his arm. His fingers flexed wide open, and a brief spark of electricity arced up the blade with a crackle.

“No.” Spooner shook his head. “No.”

Corporal Ryan’s laugh was almost hysterical. “What the hell is this? Are we all droids now or something?”

But nobody else laughed with him.

Private Doherty sighed and drew his knife. He was also a droid.

One by one, the rest of the men took out their blades and rolled up their sleeves. One by one, they all turned out to be machines.

For a while, nobody said anything.

“What about you, Sarge?” said Private Cooper.

Cameron snorted quietly. “Do I even need to bother?”

But he took out his knife anyway. He wiped it on his combat pants, then hesitated. Why had he done that? It was just habit. He smiled.

He pulled off his glove and spread his fingers. He levelled the steel blade perpendicular to his palm, then drew the silver point along his lifeline.

For a moment, he could almost believe it was blood that came off on the knife blade. In the perpetual low light of Erebus, it looked black, but he told himself it was really just a very, very dark red. The atmosphere of Erebus must have a very high oxygen content, he thought. He was over-producing haemoglobin; that’s why his blood looked so dark. But it was blood. It was - for a few moments.

Then he saw the ball of a metal knuckle beneath.

Cameron let out a deprecating cough of a laugh. “I was gonna say that hurt; but it didn’t, did it?” He looked up at his men; all of them staring at their self-inflicted wounds. “What’s pain to us? A line of machine-code; a few 0s and 1s?”

“I was in love with Daniels’s sister,” Wells said.

Slowly, the men looked round at him.

“But that’s just a few lines of machine-code, too, isn’t it? Daniels didn’t have a sister; robots don’t have sisters, so I couldn’t have loved her. All I have are memories, but even they aren’t my own, are they? Everything I’ve done, everything I’ve experienced, it’s all just a lie. None of it really happened, did it?”

Doherty grabbed his shoulder supportively.

“How in the hell am I meant to tell the difference between the real memories I have and the ones I’ve been given?” Cooper growled.

“Maybe you’re not,” said the Doctor.

Cameron shot him a look; had almost forgotten he was there.

“Meant to tell the difference, I mean.”

“Doctor, if you’ve got any TSIs, I want to hear them.”

The Doctor grinned. “Sergeant, I’m full to the brim with Ts, Ss and Is.”

“We’re listening, Doctor,” Sergeant Cameron said.

The Doctor stuck his hands in the pockets of his leather jacket, as he often did when proselytising. He felt the cool metal of the disc-shaped transmitter he’d retrieved from the reconnaissance droid; he’d forgotten it was there.

“What kind of missions are you usually sent on, Sergeant?” he asked. “I’m guessing more covert operations than rescue missions.”

“Yeah.” Cameron nodded. “Mostly.”

“Well, there you have it, then. That would make sense. You lot are the perfect soldier. You look human; you sound human; you can act human, as well, but unlike humans, you aren’t fallible. You don’t have human flaws, human weaknesses; you don’t tire, you don’t get afraid; and pain is just a stream of data. You can fight on when humans have fled or otherwise given up. Once you’ve been given your mission, you see it through. You’re relentless; and you don’t question your orders. And all the while, not even the humans on your own side can tell you’re there.”

“Yeah; sounds like us,” Cameron murmured.

The marines looked at each other, some of them nodding.

“Well, if we’re all satisfied, we can get on.” The Doctor took the transmitter out of his pocket and rolled it in his palm. “Can I have that GPS terminal?”

Private Doherty looked to Cameron for a response.

“It’s starting to make sense,” the sergeant said slowly; his eyes were flitting around the horizon. “There was no observation team, was there?”

The soldiers fell silent and stared at him.

“The terminal?” the Doctor said.

“I heard you say it, Doctor,” Cameron went on. “When Captain Hamilton asked for theories, suggestions and ideas, you said there was no ship.”

The Doctor sighed. “Occam’s Razor again, Sergeant. The simplest solution is also the likeliest. The landing zone you were given was unsuitable, there was no sign of the ship ever being here, and your GPS terminal was working properly.”

“Why…why would they send us, then?” said Doherty.

The marine with Ryan daubed on the front of his helmet said, “It was a ploy.”

Slowly the marines turned to glare at him.

“What?” said the one the Doctor had heard being called Wells.

“A ploy; a ruse; a trick,” Ryan said bitterly. “There was no observation team and the shuttle wasn’t sabotaged. We were meant to crash.”

“But why?” Doherty asked again.

Cameron snorted. “Why do they usually send robots here?”

Doherty began to say something else, but the words caught in his mouth and his face suddenly fell. The Doctor watched as they all began to understand.

“So can I have the terminal or not?” he asked.

“I guess we’re no longer top of the line,” Ryan said, looking dazed.

Wells snorted. “I’d really like to meet one of our replacements.”

Several of the others murmured in concurrence.

“Maybe they can cook and sew and juggle with fire,” said Ellison.

Ryan sighed. “How many times have we mocked the stupid droids that get tricked into coming here?” He shook his head in disbelief. “But all they had to do was give us a few fake orders and we came here willingly.”

“We always do,” Cameron muttered.

The Doctor had had enough. “Give me that.”

“Hey!” Private Doherty cried, as the Doctor snatched the terminal.

“Let him have it,” Cameron said quietly.

Doherty begrudgingly let go of the strap.

Spooner sighed. “I guess this means Elsie doesn’t exist.”

“Elsie your new girl, Spoon?” said Ellison.

He smirked. “Elsie’s a bitch; a Doberman bitch, eighteen months old. I got her before our last tour of duty. I could tell you exactly what she looked like; it’s almost as if I can see her now. My girl’s called Nancy. She’s meant to be looking after Elsie; but I guess that if Nancy doesn’t exist, then neither does Elsie.”

“I called my mom from the Reliant,” Cooper said. “But I don’t have a mom, do I? So who was I talking to? Where do all these memories come from?”

As the marines wallowed in a surprisingly human pit of despair and self-doubt the Doctor flipped the terminal over and opened the panel on the back. He was looking for the transponder picking up signals from the orbiting space-station.

“What are you doing, Doctor?” Cameron asked.

The Doctor found the transponder and unplugged it. He prised open the biscuit-shaped transmitter and tore out its own local transponder.

“Acting on a hunch, Sergeant,” he explained, then he spliced the transmitter’s transponder into the terminal’s and switched the transmitter on.

“I’m listening,” Sergeant Cameron said.

The Doctor turned the terminal back over and switched it on too. “If I’m right, and that reconnaissance droid I disabled belonged to the Cybermen, then it’ll be sending a signal back to their base. I’m bypassing the GPS signal coming from orbit and using the terminal to triangulate the position of their beacon.”

“I thought you said their base was nearby.”

The Doctor nodded, watching the screen blink. “It probably is, but we’ll need precise co-ordinates if we’re actually going to find the place.”

“Doctor, I think our priorities have changed.”

“Yours might have; mine are still to find Rose. Ah, here we go.” A large blot on the screen shrank, jumped position, then settled, flashing, in one location. He held the terminal out to Doherty. “Here; I can’t read this. Where’s that?”

“About two thousand metres that way,” Private Doherty said, pointing across the valley beneath them as another geyser erupted nearby.

Sergeant Cameron sighed. “Doctor, you saw what these Cybermen did to my platoon; do you honestly think Rose is still alive?”

“Why wouldn’t she be? She’s a living, breathing bipedal humanoid; they wouldn’t kill her when they could turn her into another Cyberman.” He frowned. “Or should that be Cyberwoman? Not sure if they have genders.”

Cameron exchanged glances with his men.

“I suspect they attacked you because they perceived you as a threat to their base,” the Doctor went on. “But they can’t turn you into Cybermen because you’re not organic. You’re just spare parts to them, I’m afraid, Sergeant.”

“Just like everything else here,” said Ryan.

Cameron shook his head and snorted. “You know what, Doctor, it doesn’t sound like these Cybermen are all that different from the men who built us.”

The Doctor lowered the terminal. “You’re quite wrong.”

“Am I?” Cameron’s mouth barely moved.

“Yes.” The Doctor gave him an unblinking stare.

Cameron broke away first, and massaged his forehead. For almost a minute, nobody spoke. The Doctor took the terminal to the edge of the precipice and tried to spot any telltale sign of the Cyberman base on the adjacent edge of the valley.

“We have to find a safe way down there,” he said finally.

“Why?” Sergeant Cameron said sharply.

The Doctor turned round. Most of the soldiers were spread out; some were sitting down. None of them were talking to each other.

“The Cyberman base is down there.”

“But what’s the point, Doctor?”

The Doctor went to answer him, but didn’t get a chance.

“Say you manage to rescue Rose; then what?” Cameron went on. “Nobody knows you’re down here, and nobody’s coming to rescue us. There’s no escape; that’s the point of this place. We’re stuck here, Doctor, and so are you.”

The Doctor frowned; the man had a point.

Working a bit like a machine itself, the Doctor’s brain chimed in with a piece of advice he’d got from a parliamentary delegate of the Democratic Bureaucracy of Western Europe and the Irish Commonwealth during a visit to Earth in 2081:

The best way to side-step a good argument is to make a completely irrelevant point that’s a better one.

“Tell me, Sergeant: how many tetrabytes of processing power are the seven of you wasting on self-pity?” the Doctor asked.

Cameron held up his hands defensively. “It’s not self-pity, Doctor; it’s just a question: even if you save Rose, how are you going to get off this planet?”

He watched as the Doctor stepped away from the precipice and handed the GPS terminal back to Doherty. He approached with an electric look in his eyes.

“I can’t tell you my plan, because you won’t like it,” he said. “But I promise you that it’ll work, Sergeant, because it’s never failed me in the past.”

“What? Been in similar situations before, Doctor?”

“Sergeant, I’ve been in so many pickles, I feel like a gherkin.”

Cameron couldn’t stifle a smirk. “I still want to hear it first.”

“I promise to detail my strategic blueprint as soon as we’re walking. Two thousand metres isn’t far, but then, my plan is a concise one.”

Cameron looked around his men, slowly, each in turn. Six expectant faces that had once only looked to him for orders were now looking to him for something more.

“You’re sure you can get us off this world?” he asked the Doctor.

“Well, I have no intention of staying here.”

“That’s not what I asked, Doctor.”

The Doctor nodded curtly. “In that case; yes.”

Cameron sighed silently. “Okay; fine; whatever. We’ll do it your way.”

“Fantastic!” The Doctor grinned.

“All right; let’s move out, marines. Doherty, you’re in front.”

Once they had got their orders, the men moved with purpose. They checked their weapons, collected spare ammunition clips, and picked up ration packs. Cooper and Ellison picked up the captain’s big grey crate without being asked.

Cameron took a last look around. Bodies littered the hilltop, but Cameron found it difficult to feel anything for them; not because they weren’t actually dead having never been alive, but because he knew his feelings weren’t actually real either.

“So what’s this plan of yours, Doctor?” he asked as they walked.

He and the Doctor were bringing up the rear.

“I’m going to make it up as I go along,” the Doctor said.

“Stick to giving straight answers, Doctor; sarcasm doesn’t suit you.”

“Who’s being sarcastic? That’s the plan.”

Cameron looked at the man; he was being serious.

“Trust me, Sergeant; it never fails.”

NOTES:
This is my least favourite chapter, even though (and perhaps because) I rewrote some of it substantially. It's the third that happens in the exact same place, and another one where people just stand around talking. Hopefully the dramatic revelations help to keep the momentum going, but at the end of the day, they're having a conversation whilst poor Rose is a prisoner of the Cybermen. On the flipside, however, part of the intention with this chapter was to introduce the marines as characters in their own rights rather than just a group, which needs to happen if readers are to care about them when things go nasty for them once more. As they're about to...

For some reason Occam's Razor came into things, the second story in a row where I've brought it up.