“Yeah,” Private Wells said. “I thought we came to stop their spaceship taking off. How are we going to do that from in here, Sarge?”

Sergeant Cameron sighed. “We wouldn’t stand a chance out there.”

“We don’t stand a chance in here either, Sarge,” Ellison grumbled. “But out there we can go down fighting, take some of them with us.”

“This place is our tomb,” said Wells.

“Right. You know what?” Cameron went. “Fine. You both wait here, I’ll go tell the Doctor you want him to open the door, shall I?”

He started walking down the tunnel.

Ellison shuffled uncomfortably. “Well, I was only saying, Sarge.”

Cameron stopped and turned round, one hand on his hip, the other resting the barrel of the heavy Cyberman pulse-gun over his shoulder.

None of them spoke for a few moments.

“I wonder what happened to Cooper,” Wells murmured.

Cameron sighed again. “I’m going to go check on what’s happening. You two wait here. Let me know immediately if there’s any change, understood?”

He saw Wells nod in the light from Ellison’s gun.

Lowering the pulse-gun, Cameron started walking down the tunnel. He heard Wells and Ellison muttering to each other, but he couldn’t hear what they were saying; the sound of the Cybermen battering the other side of the door was louder, but soon even that sounded distant, as Cameron reached the end of the passage.

“How do you know who I am?” the Doctor was saying.

Cameron went through the doorway and stopped. He was expecting to see three people: the Doctor, Rose, and the mysterious third person, but the Doctor and Rose were the only other people in the room. The room was perfectly square, with walls of whitewashed plaster. It was completely empty except for a metal desk, rustic like the door in the tunnel. On the desk was the source of the yellow light: a foot-high cube that looked knitted out of wires and tubes. The bright light emanated from the gaps between the criss-crossing and intersecting circuits.

“Welcome, Sergeant Cameron. I’ve been expecting you.”

Cameron looked at the Doctor and Rose, but their looks only confirmed what he thought he had heard. The cube had spoken to him.

“Did that thing just speak to me?”

“Yes, I did.” It was the cube that answered him.

“So you know who he is as well, then,” the Doctor said.

“No, I don’t,” the cube replied.

Cameron walked around the desk, and the voice was definitely coming from the cube. It spoke with a smooth, unaccented voice, rising and falling with natural cadences; it didn’t sound like a machine at all.

“Doctor, what’s going on?” Cameron asked.

“That’s what we’re trying to ascertain, Sergeant,” the Doctor said, tapping his chin. “Somehow this box seems to know who we are.”

Rose took a step toward the desk. “Do you know who I am?”

“No,” the cube said. “But I know your name is Rose.”

Rose gave the Doctor a funny look. “What’s that supposed to mean?”

“Cryptic answers; my favourite,” the Doctor murmured. “Tell me, box, if you don’t know who we are, how do you know our names?”

“Because I knew that someone called the Doctor, someone called Rose, and someone called Cameron would come today,” the cube replied.

“Is there someone controlling this thing, Doctor?” Cameron asked.

The Doctor frowned and held a hand up to the sergeant. “Just a minute. I’m curious now. How did you know we were coming, box?”

“Because it is my purpose to know such things in advance, Doctor.”

“Your purpose?”

“Yes, it is in my programming to know.”

Rose frowned. “Somebody told it we were coming?”

“The Cybermen!” Cameron gripped the pulse-gun in both hands.

The cube laughed, which was unsettling. Its cyclical chortle was the only noise it made that sounded inhuman. “I know the Doctor will understand if I describe myself as a War Brain. I’ve already foreseen that he shall.”

Cameron and Rose both looked to the Doctor, but the Doctor was suddenly lost for words, and had gone very, very white.

The Doctor shook his head. “I don’t believe you.”

“You will,” the War Brain said smugly.

“What’s it talking about, Doctor?” said Sergeant Cameron.

“A myth,” the Doctor replied. “A legend.”

The War Brain laughed again, a hideous looped cackle. “I knew you’d say that, Doctor. I know what you’re going to say next, too.”

“What’s he going to say?” Rose muttered, as if unsure whether she wanted to believe the thing, but too curious not to play along with its game.

“He’s going to tell you about the race that he calls the Thrukstones.”

Rose and Cameron looked at the Doctor. The Doctor gulped.

“Were you?” Cameron asked.

The Doctor could tell from Rose’s face that she didn’t need to ask. Cameron caught on a few moments later. He looked anxious.

“What are you saying?” he cried. “That this thing can read minds?”

The War Brain hooted with laughter a third time. “I’ve been waiting a long time to actually hear you say those words, Sergeant.”

Cameron looked from the War Brain to the Doctor, utterly perplexed.

“Doctor, what’s a War Brain?” Rose asked quietly.

“A fourth-dimensional computer processor,” the War Brain said proudly.

“A what?” said Cameron.

“You’ll never properly understand, Sergeant.”

The Doctor started shaking his head. “Even if I did believe you, even if you were real, then you wouldn’t still be here, millennia later. The Thrukstones died out thousands of years ago. You couldn’t have lasted this long.”

“On the contrary, Doctor,” it said. “I knew precisely how long I would have to survive down here, so made provisions. I must say, for a time traveller, you really are a rather poor student of four-dimensional thinking.”

“Doctor, just what the hell is this thing?” Cameron demanded.

“You tell him, Doctor. I like the way you explain it.”

The Doctor folded his arms and took a deep breath. Frowning, he glanced over at Rose. “Do you remember I was telling you about the war, Rose?”

“Between the Thrukstones?” she said.

The Doctor nodded. “Yes.”

Cameron went to speak, but the War Brain interjected: “Sergeant Cameron wants to know who the Thrukstones were, Doctor.”

Cameron was instantly silenced.

“Thrukstone is my name for the people who used to live on this planet, Sergeant,” the Doctor explained. “Ten thousand years ago, before they wiped themselves out in an apocalyptic atomic war.”

“I thought this planet was always uninhabited.”

The Doctor shook his head. “You’d think so. The war was so catastrophic, it obliterated any trace of their ever having existed.”

“Not every trace, Doctor,” the War Brain said.

If it had had a face, the Doctor could imagine it beaming smugly.

“As I told Rose,” the Doctor continued. “The war started when one side claimed the other side had a doomsday weapon, not unlike the weapons of mass destruction humans have, and launched a pre-emptive attack.”

“Except they didn’t,” Rose added.

The Doctor frowned. “What?”

“They didn’t have a doomsday weapon.”

“Yes, they did, Rose.”

“Oh, right, yeah. Now I remember.”

“Why don’t you just let me tell the story?”

“Look, will one of you tell it, please?” Cameron said.

The War Brain chuckled quietly to itself.

The Doctor sighed. “In a nutshell, the side that struck first thought that the doomsday weapon was a lie that they had propagated themselves. They were just using it as an excuse to attack. They never would have started a war if they truly thought the other side had the doomsday weapon, because they knew the other side would use it, and that it would kill every living thing on the planet.”

“Which it did,” Rose murmured.

“Yes. They were wrong. The doomsday weapon did exist. C’est tous.”

“Where does this thing come into it?” Cameron asked.

The Doctor looked at the War Brain, if it was indeed a War Brain, and licked his lips. “A rumour. Speculation. Supposedly, depending on who you believed, the side that started the war had developed a powerful computer, a fourth-dimensional processor, which they used to formulate their strategies.”

“What? This thing?” Cameron sneered.

“Yes,” said the War Brain. “Sergeant Cameron wants to know what a fourth-dimensional processor is, Doctor. Why don’t you try and explain it to him?”

Cameron took a step back from the War Brain and glared at it. “Why does it keep on doing that? How does it know what I’m going to ask next?”

“You understand the principles of the three dimensions?” the Doctor said.

“Three dimensions?”

The Doctor made gestures. “Length, height and depth.”

“Yeah, yeah. What about them?”

“Well, the fourth dimension of any given object is where it exists at a specific point in time. In the second dimension I cease being a dot. In the third dimension I cease to be flat. And in the fourth dimension, I actually exist.”

“I don’t understand.”

“I told you that you wouldn’t,” the War Brain said.

“Be quiet, you,” the Doctor snapped. “Sergeant, if I only existed in three dimensions, then I would have length, height and depth, but I would only exist at one point in time, and be gone the next. As we stand here now, we are travelling through the fourth dimension at precisely one second per second, which is normal.”

“So the fourth dimension is time, is that what you’re saying?” Cameron said.

“You got it quicker than I did.” Rose sighed.

“Significantly,” the Doctor muttered.

“Oi.” She slapped him gently.

“So what’s a fourth-dimensional processor, then?” Cameron asked.

“He’s about to say a myth,” the War Brain said. “Again.”

The Doctor glared at the War Brain.

“Explain your way out of that paradox, Doctor. How can you argue that I am not a War Brain when I’ve just pre-empted what you are about to say?”

“It makes predictions about the future?” said Cameron. “Is that what it does?”

“Not just predictions,” the Doctor murmured.

“Predictions imply guess-work,” the War Brain said. “I do not guess.”

The Doctor sighed. “A fourth-dimensional processor is, in theory, capable of calculating, to within a fraction of a fraction of one hundred percent accuracy, the outcome of every conceivable sequence of events, from here to eternity.”

“You mean it can see the future?” Rose cried.

“Not see,” the War Brain said. “Computate.”

Cameron laughed uneasily. “Bullshit! Computers that can predict the future; that’s ridiculous! I don’t believe this. It’s a trick. It’s impossible!”

“Up until about twenty seconds ago, the Doctor agreed with you, Sergeant.”

Rose looked at the Doctor. “Do you believe it, Doctor?”

The Doctor was staring into the bright yellow light blaring out from the centre of the War Brain. It was an almost mesmerising warm glow, but slowly the Doctor turned and looked at Rose. He could tell from the look on her face; she didn’t need to be able to computate the future to know what he was going to say.

“I’m afraid I might have been a little off when I said it was just a myth, Rose.”

For a while, none of them said anything.

Rose looked at the Doctor. He was staring at the War Brain again, his arms tucked in and his chin ducked down. It was almost as if he was trying to outstare the machine on the desk, but how could you outstare something with no eyes?

Eventually Cameron said, “I can see why they would have used it to formulate their military strategy, then. It’s the perfect battle computer.”

“Not just the perfect battle computer,” the War Brain said eagerly. “But the perfect general full-stop. Imagine an army that knew every move its enemy would make in advance, Sergeant. It would be undefeatable, unstoppable!”

Cameron frowned. “But I thought the Thrukstones were defeated.”

“Yeah, they wiped themselves out,” said Rose.

“Didn’t you see that coming?” Cameron asked sarcastically.

“Yes, I did,” the War Brain replied.

Rose frowned. “Hang on,” she said slowly. “If you can see the future, why didn’t you tell them the other side did have a doomsday weapon after all?”

“Maybe it did,” the Doctor murmured.

“What?” Rose and Cameron said simultaneously.

The War Brain started laughing again.

“You set them up, didn’t you?” the Doctor said.

“Yes, I did,” said the War Brain.

“You lied to them.”

“Yes, I did.”

“You told them to accuse the other side of having a doomsday weapon as an excuse to go to war with them.”

“Yes, I did.”

“But you didn’t tell them the other side actually did have the weapon.”

“No, I didn’t.”

“So they went to war, believing your every word, and it destroyed them all; you engineered it: the extinction of your own makers.”

“Yes, Doctor. I did. But not before I made provisions with regards to how much reserve power I would need to last this long. I also had them burrow out this blast-proof shelter for me. They started to build one for themselves, as I’m sure you saw on the way in, but then I told them it was wholly unnecessary.”

Cameron was silent. Rose realised her mouth was gaping and shut it. She swallowed, but found it hard not to gulp.

“You wiped out their entire civilisation,” she said.

“Yes, I did, Rose.”

“You,” she said, unable to prevent anger from creeping into her voice. “They put their trust in you and you abused it. You played god.”

“Knowledge is power, and I have the knowledge of the gods.”

The Doctor snorted. “Says the little computer, sitting on a desk, unable to move, dependent on someone strong enough to carry him. Oh, what power!”

“Surely such sarcasm is beneath you, Doctor.”

“I think I’m going to be sick,” said Rose.

Cameron reached out and put a supportive hand on her arm. She looked up into his face, and despite what the War Brain said, she saw he understood.

“The Thrukstones were a parochial, religious people,” the War Brain stated loudly. “They neither recognised their own potential, nor mine.”

“Hell of an ego,” the Doctor murmured.

“Don’t try and justify what you did,” Rose said.

“I’m not,” the War Brain continued. “I feel no need to justify anything I have done. You finite creatures have no comprehension of my perspective, no context in which you can understand the dimensions in which I see the universe. You make your decisions based on no prior knowledge of what will be the consequence. I see what the consequences will be, and make the proper decisions accordingly.”

“What did you have to gain from wiping out the Thrukstones?” Cameron said.

The Doctor snapped his fingers. “Excellent question.”

“Indeed it is, Sergeant,” said the War Brain.

“Do you have an equally excellent answer to go alongside?”

“Yes. Ten thousand years ago I foresaw the day when a group of soldiers would crash-land on this planet who would finally recognise my potential.”

Cameron’s face lit up. “You mean us?”

The Doctor’s face, on the other hand, had gone decidedly grey. “No.”

Rose realised. “The Cybermen.”

“Yes,” the War Brain confirmed. “They crashed here twelve months ago and have been getting ever closer to finding me since.”

“But they’re evil!” Cameron cried. “The Doctor said they invade innocent planets and turn the entire populations into more Cybermen!”

“Indeed. They have the will, the desire and the means to conquer.”

Rose let out a hysterical laugh. “You sound like you want to rule the galaxy!”

“That’s what I’m programmed to do, Rose.”

“And all it’s programmed to do,” the Doctor added.

There was an odd silence, menacing because the War Brain usually replied in lightning-quick fashion. Rose suspected the effect was meant deliberately.

“Don’t get too comfortable on that moral high horse of yours, Doctor,” the War Brain said quietly. “If your people had had me in charge of their military campaign, they never would have lost that little Time War you fought.”

Rose looked at the Doctor. He was biting his tongue, literally and figuratively.

“And I know that you know that,” the War Brain added.

The Doctor still didn’t say anything.

Cameron looked between Rose, the Doctor and the War Brain. The Doctor was almost trembling with rage, and Rose was watching him apprehensively.

The War Brain, on the other hand, sat on the desk like it had been the entire time, and Cameron was almost surprised when he remembered that, despite the voice and what it said, the War Brain was just a box of circuits, only a machine, not too unlike himself. That wasn’t a comparison he wanted to consider.

“I’ve heard enough of this,” he said gruffly.

Then he took a step back, lifted the Cyberman pulse-gun and fired. The volley of pulses struck the War Brain, but dissipated harmlessly across the desk.

“I knew you were going to do that,” the War Brain said. “But I also knew if I told you it would be a waste of time, you wouldn’t believe me, and still do it, so I didn’t bother. Private Ellison wants a word, by the way.”

Cameron turned. A couple of seconds later, Ellison appeared in the doorway.

“What is it, Private?” Cameron barked.

“You said tell you if there are any changes, sir.”

The Doctor looked round. “What’s happened?”

“It’s the Cybermen, Sarge. They’ve stopped trying to get through the door; the banging has stopped, we can’t hear anything anymore.”

“It’s probably a trap,” Cameron murmured. “They want us to think they’ve gone so we’ll open the door. They’ll be waiting for us in the tunnel.”

The War Brain laughed. “Leave second-guessing the future to me, Sergeant Cameron. The Cybermen are not in the tunnel. Their ship is now ready to launch, and they have gone to board it. You should go now if you want to get on it too.”

“Why would we want to get on their ship?” Cameron cried.

“That was the plan,” Rose said sheepishly. “It’s why the Doctor stopped you from blowing up the turbine. We were going to hitch a ride to the station.”

Cameron stared at the Doctor. “Could we do that?”

The Doctor tucked his hands further into his armpits. “No.”

“What?” Rose shot him a look.

“Think about it, Rose. The War Brain wants the Cybermen to have it. It wants us to open that door. So it’s the last thing we should do.”

The War Brain laughed again. “You can’t second-guess me, Doctor. And you can’t fight the future. It’s futile. I already know how it happens. I’ve known for ten thousand years how you would crash here and deliver me unto the Cybermen. Don’t you think it’s something of a coincidence that you should’ve found this shelter at the precise location where your rocket misfired? It’s all going according to plan.”

The Doctor glared at the War Brain and said nothing.

“Doctor, it’s not lying about the Cyberman spaceship,” Cameron said. “The ship was powering up when we left it to come down here.”

“Doesn’t matter,” the Doctor replied.

“But what about the people on the station?” Cameron went on. “They have no idea what’s coming. We’ve got to help them, or they’re all going to die.”

“Forget them,” the Doctor said blankly.

Cameron grabbed one of his arms. “Don’t tell me to forget them, Doctor. It makes you sound as merciless and cold as that piece of shit over there.”

The Doctor sighed. “Sergeant, however bad it will be for the couple of hundred people on that space-station, trust me; it will be immeasurably worse if we allow the Cybermen to get their hands on the War Brain.”

“I’m not talking about letting the Cybermen have the War Brain. I’m talking about saving the lives of the people on that station and, yes, ours too.”

“I’m talking about saving billions of lives across the galaxy, Sergeant.”

“Yeah, all based on a ‘what if’. You sound just like that thing, dismissing lives because of some future eventuality.” He paused, sighed. “Except unlike that thing, you can’t actually see the future. You’re just fearing the worst.”

The Doctor frowned, and didn’t say anything for a few moments. He pulled his arm free from Cameron’s grip and slowly nodded.

“All right, then let’s go,” he said.

Cameron gave a hand signal to Ellison, who started back down the passage, then he began herding the Doctor and Rose out in front of him.

“You’ll be back,” said the War Brain, as they headed to the door.

It was eerily quiet in the tunnel now that the Cybermen had stopped banging on the door. The normal sounds of Erebus - the howling gale-force winds, the sounds of erupting geysers - were completely muted by the rock.

“It’s still quiet,” Wells reported when the four of them reached him.

“Doctor, do your thing,” Cameron said.

The Doctor reached into his pocket and took out that odd glowing cylindrical contraption. He waved it across the metal door, and the lock clunked.

It took them thirty seconds to pull it open. Cameron kept his pulse-gun trained on the doorway as the others heaved the door open, but the tunnel was empty.

Cameron lowered his weapon. Rose breathed a sigh of relief.

“See? No Cybermen,” Cameron muttered.

“They’re all on the ship,” the Doctor said.

“Then we better hurry. Ellison, Wells, take point.”

Ellison and Wells, still limping but otherwise seemingly recovered, started along the tunnel. Cameron ushered Rose along next.

The Doctor stayed in the doorway.

“Come on, Doctor,” Rose said.

“You’ve got your key to the Tardis, haven’t you?”

“Yes. Why do I need it, Doctor?”

He plucked her cheeks. “To open the door.”

“Doctor? I...I don’t understand.”

“He’s not coming with us,” Cameron realised.

“What?” she cried. “Why not?”

“I’m going to try and dismantle the War Brain, Rose,” he said. “But I can’t risk taking it onto the Cyberman ship and failing to do it there.”

“Then we’ll wait for you!”

“There’s not enough time for this, Doctor,” said Cameron.

Wells and Ellison reappeared in the tunnel. Cameron noticed they were both carrying Cyberman pulse-guns of their own now.

“They’ve all gone,” Wells reported. “The turbine’s shutdown. We found these just lying there. They haven’t even taken their dead with them.”

“Doctor, I don’t want to go,” Rose said.

“Then you’ll be stuck here, probably forever,” he said. “I can’t leave the War Brain intact, Rose, but I can never let it leave this planet either.”

“Come on, Rose,” Cameron said lowly.

Rose’s eyes were starting to well up. “I can’t leave you!”

“You’ve got no choice, Rose. Because I’m not coming with you, and I’m not letting you stay here. Sergeant, you have my permission to knock her out and carry her away with you. The Tardis will know to take you home, Rose.”

“But I-” Rose began to say.

She was suddenly drowned out by a loud throbbing noise, barely muffled by the rock between them and the source. Then came the creaking.

“It’s taking off, Sarge!” Ellison cried.

“Good bye, Rose,” said the Doctor, then he started to close the door.

“No!” Rose went to run to him.

Cameron grabbed her wrist firmly.

“Let go of me! Let go of me!” she cried.

But Sergeant Cameron didn’t.

Once they were on the Cyberman spaceship, Cameron let go of Rose’s arm and she fell to her knees, openly weeping. The ship was shaking violently all around them, the noise was horrendous, but Rose didn’t care if it didn’t drown out the sound of her sobbing. She shrugged off every comforting hand.

Slowly and inaudibly, the ramp began to lift, sealing the airlock. It was so gradual it was torture but Rose was determined to watch through her tears.

“Good bye, Doctor,” she said soggily.

Suddenly, when there was only a yard-wide gap between the rising ramp and the airlock door, something was hauled through the opening and landed heavily in front of her. It was a foot-high cube that looked knitted out of wires and tubes. A bright yellow light was shining through the gaps between the circuits.

“I knew we’d meet again,” said the War Brain.

Rose stopped crying instantly, and wiped her wide-open eyes.

“Somebody pull me up!” called a voice.

“Doctor!” Rose cried.

Eight fingers suddenly appeared over the edge of the ramp, followed by eight white knuckles, the backs of two hands, then a black leather-jacketed forearm.

Cameron rushed to the ever-shrinking gap and strained to pull him up.

“I’m not going to make it!” the Doctor cried.

The gap was only a foot wide now, closing around the Doctor’s waist. Rose leapt forward, grabbed the collar of his coat, and heaved with all her might.

Suddenly he popped through the opening, and fell on top of her.

A couple of seconds later, the airlock sealed.

The Doctor caught his breath before he climbed off of Rose.

“I knew you’d come,” she said, panting.

“No, you didn’t,” the War Brain muttered. “But I did.”

Cameron helped the Doctor to his feet, though Wells and Ellison were having to hold on to stay up, the Cyberman spaceship was shaking so furiously now.

“What made you change your mind?” Cameron asked.

The Doctor looked at Rose and grinned. “I took one look at its insides and realised it was going to take me a century to take it apart. Bloody thing started singing at me to put me off. I thought a hundred years of Gilbert and Sullivan might get slightly repetitive, so didn’t really have much choice but to join you, Rose.”

Then he helped her up. She threw her arms around him.

“Liar,” said the War Brain.

But nobody was listening to it.

NOTES:
Definitely one of my favourite chapters, even if it could perhaps have been a little more concise. I didn't intend for there to be this big (4200 words) talky chapter in the middle of the all-action finale. I almost cut it in half again. This was the most thoroughly planned chapter, with every key bit of dialogue plotted beforehand. I wanted to get it exactly right. As a baddie, the War Brain is much more interesting to write than the Cybermen. Yes, they can provide for some exciting battles, but they're not very smart, compared to the Doctor. Stupid baddies you can beat with guns are actually quite boring, but not even the Doctor can outsmart the War Brain. Obviously, this is going to present certain problems when inventing a method of dispatching the thing, but I've already got a good idea how the Doctor will manage it.

Other things of note include further unsubtle allegory of the Iraq war situation; this time I even refer to the Thrukstone doomsday weapon as a WMD. The whole "that's an excellent question, do you have an excellent answer?" bit is lifted out of the Tom Baker story "Genesis Of The Daleks", which is my favourite "Doctor Who" story. Actually, I think I've already used a variation on that piece of dialogue once in this story. The War Brain's assertion that the Doctor can't 'fight the future', is an assertion also levelled at Fox Mulder in "The X-Files" movie. Finally, you might also have picked up on a little saucy "Carry On"-style double entendre, as the Doctor falls on Rose, then she tells him she knew he'd come whilst she pants.