"Back up slowly," the Doctor whispered, briefly squeezing Rose's hand, "and get inside the TARDIS as soon as you can."
"You know what we want, Doctor," the mechanical voice droned.
"I know," the Doctor replied, keeping Rose behind him as he took another small step back, "but I'll need time to find--"
"You have five minutes. No more."
"Wait! That's not--"
"FIVE MINUTES. One second longer and we WILL kill them."
"Five minutes," the Doctor nodded, urging Rose into the TARDIS, as he followed her, still edging his way backwards.
"FOUR MINUTES AND FIFTY-TWO SECONDS."
As soon as he was inside, the Doctor quickly closed the doors, exhaling sharply as he went over to the console and began fiddling with the controls.
"Those robots--" Rose started.
"Cybermen," the Doctor corrected, as the TARDIS de-materialised.
"Those Cybermen," Rose said, "Will they really kill those people?"
"Oh, yes," the Doctor answered, "They could kill everyone on that planet without so much as blinking an eye," he paused for a second, then added, "which they don't do anyway," he paused again, "Blink that is."
"And you know what it is they want?" Rose asked.
"Yes," the Doctor nodded absently.
Rose waited for him to continue, but he just stood there, staring at the console, clearly lost in his own thoughts.
Realising that nothing else was forthcoming, she asked, "What DO they want?"
"Oh, right," the Doctor said, "They want to know the location of one of their outposts that they, sort of... lost."
"And you know where it is?"
"I should," the Doctor said, smiling, "I'm the one who lost it for them."
"Where are we going then?" asked Rose, still unsure of exactly what was happening.
"Going?" the Doctor said, "We're not going anywhere. I just needed some time to think."
"But you said you already know where it is."
"I do," the Doctor said, "but that's not the problem." This time he seemed to pick up on the fact that Rose was waiting for more, and continued, "The problem is what could happen if they get it back."
Rose waited silently for him to explain, resisting the urge to ask more questions.
"The Cybermen lost their last war, badly. There are only a few of them left, scattered across the galaxy. The ones on this planet probably make up more than half of what's left. With the resources from that outpost, they could start increasing their numbers again."
"You mean build more Cybermen?"
"Not exactly," the Doctor said, shaking his head, "Cybermen don't build more Cybermen. They capture others and change them into Cybermen."
"They used to be people?"
"Yes. That's why it would be a really bad idea to tell them where that outpost is."
"What are you going to do then?" Rose asked.
"I don't know yet."
"Aren't we running out of time?"
"Out of time?" the Doctor said, breaking into a smile, "No. Technically I suppose, we are 'out' of time, but we're certainly not running out of it." Seeing Rose's confusion, he tapped her gently on the forehead, "You're still thinking three-dimensionally."
"I don't understand."
"The TARDIS is a time machine, remember?" the Doctor said, still smiling, "We can take as much time as we need, and still be back before time is up," frowning slightly, he added, "I'm going to have to make a decision sooner or later though."
"If you don't tell them what they want to know, they'll kill everyone, right?" Rose said, "So, what will happen if you DO tell them?"
"The Cybermen will build up their forces and may start to pose a serious threat again."
The Doctor looked at Rose and smiled again, as he began setting the controls. "Right then. I'll just have to see to it that they don't."
"We're going back?"
"We're going back," the Doctor said, "We'll materialise immediately after we left."
"Are you sure you can do that?"
"Absolutely," the Doctor insisted, "In fact, we'll be back so soon the Cybermen may not even realise we ever left."
"Yes?" the Doctor said, turning towards her. When she didn't say anything, he prompted, "Go ahead."
"It's just... the last time you said that, 12 hours turned out to be 12 months."
"Look, Rose, I apologised for that. I'm really sorry."
"I know, but this time you've only got five minutes."
"That was just a mistake, a glitch. It can't happen this time."
"Can't happen," the Doctor repeated, beaming his most disarming smile, the one that somehow made you almost willing to forgive him anything.
Rose returned the smile, and the Doctor set the final controls.
"Here we go," he said.
There was a sudden, horrible crashing noise and Rose found herself being thrown violently to the floor.
"No no no no NO!" the Doctor shouted, frantically grabbing the console.
"That's not right at all," he muttered, checking the controls.
"We're too late?" Rose asked, getting to her feet.
"No," the Doctor replied, staring past her, "Too early."
Rose turned to follow the Doctor's gaze and let out a quiet gasp.
There in the corner of the control room stood a very familiar blue police box.
"The TARDIS," the Doctor said, "We arrived at the exact instant we were leaving."
"And now... the TARDIS is... inside... itself?" Rose asked, trying to grasp the bizarre situation.
"Yes," the Doctor said, looking worried.
"And that's bad?"
"What about the Cybermen?"
"We're caught between two moments in time," the Doctor explained, "No time's passing for them."
"Well, that's a good thing, right?" Rose asked, but from the Doctor's expression she got the feeling that it probably wasn't.
"If I could just..." the Doctor tried several more controls, eliciting a brief shudder from the console, before it fell silent again, "No, that's no good. They're trying to leave while we're trying to arrive. There's nowhere for us to go."
"Them," the Doctor said, pointing at the other TARDIS, "Us."
"We're inside there?" Rose asked, confused again.
"Yes," the Doctor replied, "Probably trying to work out why the TARDIS can't fully de-materialise."
"Because it's inside our TARDIS?"
"So, what's out there then?" Rose asked, pointing to the door.
"I don't think you want to look out there," the Doctor warned.
"Why? Is it dangerous?"
"Not dangerous, no."
Rose cautiously opened the door, revealing the back wall of the TARDIS control room. She looked back at the other TARDIS and then quickly closed the door.
"I thought that TARDIS was inside this one."
"It is, but this one's inside it as well. They're both trying to occupy the same point in time and space, and they've ended up inside each other."
"But that doesn't make any sense!" Rose exclaimed.
"Of course not," the Doctor said brusquely, "You lot are always insisting that the laws of the universe should change to match your expectations. I tried to tell Niclas the same thing, but he didn't listen."
"Niclas Kopernik," the Doctor prompted, "Copernicus. Told everyone that the Earth wasn't the centre of the universe. Made a lot of people very angry."
"Look, Rose," the Doctor said, a bit more gently, "You're just going to have to trust me on this. Each TARDIS is stuck inside the other, and neither of them can go anywhere."
"Okay," Rose said, "Well at least--"
She was interrupted by an increasingly loud rumbling noise, followed by another ominous-sounding crash.
"Oh no," the Doctor said, "It's starting already."
"What's starting?" Rose asked, "What was that?"
"There's not enough room for another TARDIS in here, so it's started ejecting rooms."
"Ejecting rooms? Where do they go?"
"Nowhere. They're jettisoned into a collapsed n-space. They cease to exist."
"So, they're being deleted?"
"Not deleted exactly. Matter can't ever really be created or destroyed," the Doctor said, pausing to think, "It actually just reduces the probability of the room's existence to zero... The net result is the same though."
"When will it stop?" Rose asked, raising her voice slightly, over the continued rumbling.
"It won't. There will never be enough space for both of them to co-exist. The TARDIS will just keep dropping rooms, until only the control room is left."
"And then... it will remove that too."
"What about us?" Rose asked, alarmed.
"We won't exist any more either, but that's not the bad part."
"Dying's not the bad part?"
"Not the worst part anyway," the Doctor said, "The TARDIS will just keep collapsing in on itself, drawing everything into this one point of time and space. Eventually, it will destroy everything."
"Everything?" Rose asked, "You mean the whole Universe?"
"Everything," the Doctor said quietly, "All of Time, past and future. Nothing will have ever existed."
"So you're a little off on your sums and the whole Universe blows up?!"
"Implodes actually, but yeah, that's pretty much it."
"Shouldn't there be some kind of fail-safe or something, to keep this sort of thing from happening?"
"There was," the Doctor said, as the TARDIS shook again, "I took it out a long time ago."
"You took it out?"
"It stopped working," the Doctor shrugged. Seeing Rose's accusing stare, he added, "Look, it's not like I can just pop in for repairs somewhere! I couldn't fix it, so I used the parts to keep everything else working."
"I'm sorry, Doctor."
The TARDIS shuddered again, and the Doctor slammed his hand against the console. "Think think think!" he mumbled angrily.
While the Doctor alternated between muttering crossly to himself and trying various switches and levers, Rose walked over to the other TARDIS.
It was disconcerting to think that there were actually other versions of the Doctor, and herself, inside there. She cautiously reached out and placed her hand against the surface. She wasn't sure what she was excepting, but she didn't feel anything unusual.
"Doctor?" she said, walking back over to the console.
"What are they doing in there?"
"Them. Us. Inside the other TARDIS."
"Oh," the Doctor said, "Well, if I know me, I'm probably trying to work out a way to undo this mess."
"Is there anything he CAN do?"
"No," the Doctor said, shaking his head, "As long as we're trying to materialise, there won't--"
He stopped talking, and then suddenly broke into a wide grin and kissed Rose on the top of her head. "Rose Tyler, you're a genius!"
"You are," he said, smiling again, "Let's go."
"In there," the Doctor said, pointing at the other TARDIS, "I think it's time I had a little talk with myself."
"What's wrong?" the Doctor asked.
"It's just... last time there were two of us..."
"Rose," the Doctor said softly, "This is different. I promise."
Rose just looked at him, her mind suddenly filled with memories of that awful day, and the large ominous creatures that had appeared in the sky.
"I promise," the Doctor said, smiling again.
Rose followed the Doctor around to the door of the other TARDIS. As he reached for the door, she asked, "Shouldn't we knock or something?"
"Why?" the Doctor laughed, opening the door, "It's my TARDIS."
The Doctor and Rose stepped into the control room to see another Doctor and another Rose, standing beside the console. Even more disturbing was the TARDIS, innocently sitting in the corner.
"Hello," the Doctor said, sounding far too cheery for the situation they were in.
The other Doctor looked up, and they began speaking to each other in some kind of strange, abbreviated conversation, made up of incomplete sentences.
"Collision?" the other Doctor asked.
"Spatial overlap," the Doctor said, nodding.
"Returned too soon?"
"A bit, yeah."
"Doctor," the other Rose interrupted, "What's happening?"
"Just what I thought," the other Doctor said, "They cut it too close coming back, and now the TARDIS is stuck inside itself."
"So you were showing off then?"
"Not me, him." the other Doctor insisted, pointing at his counterpart.
"But isn't he you?" the other Rose insisted.
"Yes," both Doctors answered together.
"I don't understand."
"You're still thinking three-dimensionally," Rose said, startling her other self.
The Doctors smiled briefly at each other, then continued their earlier conversation.
"You tried to shut down?"
"Just one," the Doctor said, winking at Rose, "We try shutting down at precisely the same time. You stop trying to leave, exactly as I stop trying to arrive."
"Of course!" the other Doctor exclaimed, "If we time it just right--"
"My TARDIS should--"
"Just bounce off."
"Because your TARDIS will already be there."
"Only now it won't be partially de-materialised."
"Thanks. Rose gave me the idea."
"Really?" the other Doctor said.
The Doctor nodded.
"Good work," the other Doctor said to his Rose, who still looked confused.
"Time to go," the Doctor said, motioning for Rose to follow him.
"Goodbye... Doctor," the other Rose called out.
"Goodbye, Rose," both Doctors replied, at the same time.
As the TARDIS door closed behind her, Rose turned to the Doctor. "That was very weird," she said.
The Doctor just smiled and went over to the console. He stared intently at several instruments for a few seconds and then threw a switch.
The TARDIS lurched and then there was a loud pop and the other TARDIS vanished.
"Did it work?" Rose asked.
"I think so..." the Doctor said, checking the console, "Yeah, it worked."
"That's a relief."
"I think we're due for a little relaxation," the Doctor said, "I know this great little cafe where--"
"What about the Cybermen?" Rose interrupted.
"What about them?"
"Don't you still have to go back and tell them where their outpost is?"
"Why do we need to go back?" the Doctor said, "We never actually left."
"You mean the other TARDIS?"
"That's right," the Doctor said, "I'm sure I can handle the situation just fine."
"The other you."
"But won't that change history?"
"No," the Doctor said, "I mean not in the way you're thinking. Not like... before. Our personal timelines are intact, which is what really matters. We're here, and they're back there."
"But isn't that a problem?"
"That there are two of you now... two of us."
"Oh that," the Doctor said, smiling warmly, "No, that's not a problem. That sort of thing always sorts itself out."
Rose didn't say anything, but her expression betrayed the fact that she was clearly troubled.
"It bothers you, doesn't it?"
"That there's another me out there? Yeah, it bothers me a little."
"Okay," the Doctor said, "Think of it this way then. Remember when we went five billion years into the future?"
"Well, there's a Rose Tyler there... and there's one in Victorian Cardiff, and in every time you've ever existed."
"Because of the TARDIS."
The Doctor shook his head. "No. Even before that. There was a Rose Tyler five years before you met me, and five years before that, and five years before that."
"But that was the past."
"And so is the one back on that planet."
"But, Doctor, I actually met her. You even talked to the other you."
"It wasn't the first time."
"You've met yourself before?" Rose asked.
"Not very often, but yeah. A few times."
"And it always sorts itself out?"
"It always sorts itself out," the Doctor said reassuringly, then paused for a moment as he set the controls, and added, "Well... ALMOST always..."