A/N: This is my first ever Who fanfic, and I have to admit, I haven't really planned much for it. It'll depend on the feedback I get for me to even continue the story for long. So please read&review!

When Two Worlds Collide

by Cecilia Green

Chapter 1: An Unexpected Visit

Rose looked around the living room. "John!" she called.

"I'm in here!" came a voice from down the hall. Rose mentally kicked herself for not looking in the workroom, since John spent about 90% of his time there. She walked briskly down the hall and poked her head through the door to see her husband hunched over a counter, fiddling around with a piece of machinery.

"What's that?" Rose asked, stepping forward to get a better look.

"This, my dear Rose, is the new and improved sonic screwdriver," said John, not once taking his eyes off of the small silver instrument. "Or it will be, if I can just get this reactor to stabilize…" he continued. Human technology is so limited, John thought to himself. It was true, for he could think of a hundred different ways to make a hundred different sonic screwdrivers, and all of them would take a relatively short amount of time, too. However, all of them required some special type of rock or gem or metal, all of which were not available on Earth.

Rose smiled. John had talked about making a new screwdriver for some time, but it had never really occurred to her that he had already gotten started. "It's getting late," she remarked, looking at the clock on the wall that now read 9:27 PM. "Are you getting hungry? I could whip up something quickly. What should we have?"

John paused in his work to give his wife a wonky smile. "That depends on what you're in the mood for," he said, taking off his pair of black glasses and setting them on the counter. "I could make us some Chicken Cordon Bleu. Or how about Canard á la Rouennaise? Fillet mignon?"

"Fish and chips?" Rose said with a smile as she bent down and gave John a sweet kiss on the lips. They stayed there a while, relishing those precious moments when they were together.

"Ah, if you want to be boring about it," said John when they finally broke apart.

"We could invite Mum and Dad over. It's been a while since we've had any other living organisms in this house," said Rose jokingly.

"Sounds like a plan, love," John replied, turning back to his screwdriver and putting on his glasses.

"Right. I'll go pick up dinner, and then we can ring up Mum," said Rose, heading towards the doorway to get her jumper.

"I'll be right here," John called after her.

Rose grabbed her black leather jumper (a style that she had picked up from the Doctor) and headed towards the front door. Upon opening it, she gave a small shriek.

On the other side stood three people. Well, there stood two people, who were carrying a comatose third person in their arms. There was a pale, round-faced girl, probably in her mid- to late-twenties, with dark auburn hair that fell in thick curls over her shoulders, and a skinny man with short, dirty-blonde hair, also in his twenties. The blonde man carried the upper part of another man, who had a large nose, a defined chin, and a messy pile of dark brown hair tossed about his head. He wore dark brown trousers, a pale brown jumper, and a bright red bow tie, which was partly burnt, as was his shirt, which Rose guessed was once crisp white.

"Are…you…Rose Tyler?" panted the girl with wild eyes. Rose noticed a distinct Scottish accent.

"Yes. W-who are you?" Rose stuttered, still in shock.

The girl didn't answer, but instead stumbled into the room, with the man following close behind, so as not to drop the big-chinned man. "Please…" she said. "He… he said you would help."

"Wait – who is that? What are you doing here?" Rose demanded, regaining her senses.

"Rose? What's going on?" said John, entering the room. He froze in his steps as he saw the three strangers. "Who are these?" he said, eyes widening.

The blonde man spoke up. "I'm Rory, and this is my wife, Amy."

"And your friend?" John nodded at the unconscious man, who Amy and Rory were now setting down on the sofa.

"He's the Doctor," said Amy.

There was silence, and John's heart nearly stopped (which would've been bad, since he only had one).

"Doctor…who?" Rose said slowly, though there was this creeping feeling that she already knew the answer.

"Just the Doctor. Don't you know him? Well…" Amy paused. "He said you wouldn't recognize him, but that you knew him. Does that make sense? I didn't entirely understand, but…" She trailed off, confused.

Rose looked at John, and John looked at her. They both looked back at the two strangers and the third supposedly-not stranger. "What?" John sputtered.

John moved his stethoscope on either side of the unconscious Doctor's chest. There were several medical books and tools strewn about the house, for John had gotten a medical degree at King's College Waterloo and was now an actual medical doctor. "Both hearts have a quick, but steady beat," he said. He then produced a small torch from his pocket and shined it in his eye after lifting the lid. "Pupil dilation seems normal." He inspected the head and soon came across a large, multicolored bruise just above the right ear.

John stood up from his crouching position next to the sofa and turned to Amy, Rory, and Rose, who were sitting in a circle of armchairs nearby. "He seems alright," he reassured them. "No apparent signs of concussion. He should be a bit dazed once he comes around, but he'll be fine." He walked across the small space between him and his wife and took the seat next to her. "Now, why don't you tell us what happened?" he said.

Amy and Rory looked at each other. What a strange sight, Rose thought. Two young adults, both with burnt and crinkled clothing, with their faces smudged with dirt and soot, sitting in armchairs and sipping from mugs of tea. But then again, if what they claimed was true and the strange man on the sofa really was the Doctor, then that picture wouldn't be unusual in the slightest.

"Um, we were in the TARDIS," Rory began.

"Somewhere in the Sylandrome System," Amy interjected.

"Right. And I remember the TARDIS took us there because it sensed a weak spot in the… the, um, layer that separated our dimensions. We were about to patch it up when a spaceship showed up, because they saw the TARDIS on their sensors," said Rory.

"Were you able to identify the type of ship it was?" John asked.

"The Doctor said it was some sort of Pit-, um, Pita-… I can't pronounce it," said Amy.

"Pitastrangalorathoris," John guessed.

"I… think?" said Rory.

"Sorry, go on," urged Rose.

"Anyway, they saw the TARDIS and fired at it," said Amy.

"But that doesn't explain how you got into our dimension," Rose put in.

"They missed," said Rory. "It just so happened that they missed the TARDIS and instead hit the little blip in space where the layer was weakest. It created a crack in the dimensions and we got sucked in."

"So you started to crash," said John. "The amount of energy needed to pull the TARDIS into another dimension would've at least squabbled the controls. You couldn't fly it."

"Yes, that's what the Doctor said," Amy said. "He was able to make sure we landed in London, but he couldn't do much more than that. He said, 'If Rose Tyler is around, she'll help.' He showed us the address, and we crashed. He must've banged his head or something, but we carried him out of the TARDIS and looked for you."

"Well, it's fairly simple from now. Once the Doctor wakes up, we'll help you patch up the TARDIS and then you can seal the crack," Rose suggested.

Amy and Rory shifted uncomfortably in their seats. "There's more," said John. Rory nodded.

"The Pitastraga-somethings… We're pretty sure they went through the crack, too," he said.

John's eyes widened as a sudden realization came to him. "A ship that can generate enough power to blow a hole through space-time has to have been enormous. If it got sucked through the crack, then the sheer size of the ship would've expanded it." He looked at his wife. "The crack is getting bigger. If we don't seal it soon, the two universes will collide."

"We'll be blown to pieces," Rose said with a stunned expression.

"And on top of that, we have the Pitastraga-somethings after us," John added.

"But why are they chasing us?" Rory asked. "Maybe we could reason with them."

John shook his head. "The Pitastragalorathorises leave the rest of the universe alone so long as the universe leaves them alone. They're pretty independent, but very territorial. If the TARDIS took you into their air space, then they're not going to stop hunting you until they're sure you're dead."

Amy peered at John suspiciously. "How do you know so much about aliens?" she asked. "The Doctor said Rose Tyler would help. He didn't mention anybody else. Who are you?"

"He's the other Doctor," said Rose.

"The Doctor?" Amy and Rory asked simultaneously.

"Doctor John Smith," John said quickly. "As in MD. I married Rose a few years ago. She told me all about the Doctor and the TARDIS." Amy and Rory nodded in understanding. Rose gave her husband a strange look, but said no more. "We can't afford to wait much longer before sealing the crack," he continued. "Hopefully, the Doctor will be awake by tomorrow morning. We'll decide what to do then." He paused for a moment. "There's a spare room down the hall, right next to the loo. We only have one, though, so…"

"One room is fine," Rory said hurriedly.

John nodded. "Right, then. I suppose we'll see you tomorrow."

"See you tomorrow," Amy said, setting her tea mug on the table. Rory did the same, and they stood up. Hand in hand, they started down the hall to their room. "Oh! And thank you, Rose. Nice to meet you Mister Smith," Amy said over her shoulder.

"Pleasure's mine. Goodnight," John called back.

Once they heard the door shut to the guest room, Rose turned to her husband. "Why didn't you tell them who you are?" she asked.

"They don't need to know just yet," John said absent-mindedly. The truth was that he didn't really know why he didn't tell them. Maybe it was because it was too hard to explain. Perhaps it was because John didn't consider himself the Doctor anymore, with one heart, no TARDIS, and only half of a sonic screwdriver. Or maybe it had something to do with the fact that the real Doctor, the Time-Lord Doctor, had regenerated. At the thought of this, John found himself staring at the unconscious Doctor, who was buried underneath a massive heap of blankets.

Rose saw him, and turned to look at the familiar stranger lying on her sofa. "Strange, isn't it?" she said. "I can never get over the whole regeneration thing. It's like… you've known a man for so long, grown on him, loved him, and just when you think you've lost him, some new one comes around claiming to be the same."

John looked at her and smiled sadly. "Is that what you thought? When you first met me?" he asked.

Rose leaned over her seat and kissed John affectionately. "No. It's the same package. You're the special deal," she said.

John pulled back after a few seconds. "What I wonder is…would that be me? If I was still the same Doctor, the same Time-Lord, would I have died? Would I have regenerated into some stranger and come knocking on your door?" he said quietly. It did trouble him, for it was fact that he was the Doctor. The only difference was that he was human. And it is never nice to know that you died. Even if there are two of you.

"But you're not the same Time-Lord. You're my Doctor, and you're here with me, and you're going to stay here with me for a long time," said Rose, squeezing John's hand tightly. They sat there for a while, and John was reminded of how much he loved Rose, how much he would do for her. The silence was broken by Rose sighing. "You're going to have to tell them. When the Doctor wakes up tomorrow, and he sees you, you'll have to tell them," she said.

"Then I'll tell them tomorrow. It'll probably be easier with the two of us anyway. But until then, we can all rest," John replied, giving a pointed look at the limp body of the Doctor.

Rose giggled. "Do you want to know what my first thought was when Amy and Rory said that that was the Doctor?" she asked.

"What?" John said curiously.

"I could only imagine your disappointment when you realized that you weren't ginger."

That got a laugh out of John, and Rose's smile widened. "Come on, love. Let's go to bed," she said. John nodded and got up from his position next to his wife, and they both began towards their room. "I love you, John. You know that? Nothing will ever change it," Rose said as they neared their bedroom.

"I love you, too," said John. They shared one last kiss, and disappeared behind their bedroom door.

Amy and Rory were in their bed. Luckily, it was a queen size, and while it was snug, they both managed to fit underneath the covers. They were lying down, facing each other. Rory appeared fast asleep, but Amy was the exact opposite. The crash was still burned into her mind…

The TARDIS rumbled and groaned, and suddenly, it felt as if the floor was yanked from under their feet. They were falling through space. "Doctor! What's happening?" Amy shouted over the TARDIS's blaring alarm.

"We're crashing! I – can't – fly her!" he grunted, spinning controls and pressing buttons on the control panel.

"Crashing? In space?" Rory yelled.

"Hurdling through the dimensions! I can make sure we land on Earth – London, if we're lucky." He paused, and his face adopted a thoughtful expression. "Rose will be there," he said.

"Rose?" Amy said. The Doctor had spoken of his old companion a few times, but never more than a sentence or two, as if the memory was too painful to mention.

The Doctor snapped out of it. "Rose Tyler! If I can just pull her up…" He typed in a few commands and the name 'Rose Tyler' popped up on the monitor, along with an address and phone number. "There! If Rose is around, then she'll help us." But he had a tone of restraint in his voice, as if seeing Rose would mean more than he let on.

Amy opened her eyes. She hadn't realized she had fallen asleep. "Rory," she said in a hushed whisper. "Are you awake?"

Her husband groaned shifted a little in his sleep. "I am now," he mumbled.

"Sorry," she said, and hesitated. "What do you think of John?"

"He seems nice," Rory replied sleepily.

"No, I mean why do you think he knows so much? And how much does he know?"

"Rose told him. I thought he explained it to us, Amy."

"But it's not just that. You heard him. The way he talked about the TARDIS was so…familiar. And I doubt even Rose knew about the Pitastranga-somethings," Amy insisted.

Rory turned to look at his wife. "What are you getting at?" he asked.

"I think there's more to John than what he's telling us. And I want to know what."