John almost walked straight into it. A blue box. Right there in the middle of the street. No one seemed to find it odd and John didn't even seem to have been aware of it, before he crashed his nose into it. Even now, when he finally saw it, he didn't seem all that interested. He scowled at the box for having stood in his way and then walked over to the edge of the street, planning to get a cab.

Sherlock however had lost all interest in the case Lestrade had brought to their attention. Certainly, a severed foot sounded intriguing enough, but there was something about this blue box that was even more interesting than detached limbs.

Sherlock circled it. A police box, as he'd expected. He recognised the old design, though he wasn't sure where his mind had collected that particular piece of useless data. He blamed John, since meeting him, Sherlock's mind was being force fed useless information every day. He had no desire to know who the contestants of the latest televised talent shows were, but now he did. And he had no desire to know how many planets there were in the solar system, but now he did.

"Hey, I've seen that before!" John had finally noticed Sherlock wasn't in the cab next to him and had gone back to see what Sherlock was up to. "I've seen that before," John repeated while circling the blue box.

"You almost broke your nose on it, so I would hope so," Sherlock said.

John shook his head. "No," he said very seriously, "I think I've seen it before, when I was a kid."

"I highly doubt it," Sherlock said. "Police boxes have been out of style for a few decades already."

"No, I have," John said. His brow furrowed as he circled the box again. "I think it was on TV," John said. He stood still and stared at the small white plaque that told them it was free to us. "And…," John hesitated and almost doubted his own memories, because they didn't seem to make sense. "And, there was a man inside."

"In the police box?" Sherlock asked sceptically.

And before John could try to argue his point, it was proven for him by the door of the blue police box being slung open - causing John to almost break his nose again - and a man appearing from inside the box.

"Oh, hello," the young man said.

Sherlock looked at the odd slightly dangly figure. He looked like a professor would in a cartoon, just 40 years too young. Student. Likes to think himself old fashioned. Probably part time actor. Most likely a…

"Err… hello," Sherlock's deduction was interrupted by John's greeting. John stuck out his hand, "I'm John."

"Hello John, nice to meet you, I'm the doctor."

"Doctor who?" John asked.

"Just the Doctor," the young man said and grinned. He pushed his quiff away from his face.

"Err… okay," John said hesitantly, then turned his face to Sherlock.

"Could you tell me which year it is?" The Doctor asked John.

"Which year?" John asked confused.

"If you would, please." The Doctor grinned again and John was starting to feel exasperated. Somehow, this guy had the same effect on him as Sherlock did. Perhaps Sherlock should share his flat with this guy. The Doctor and the Sleuth, they would suit each other nicely.

John let out a sigh and gave up trying to be the sensible one in the conversation. "Sure," he said, "it's 2010, for now…"

"For now?" The Doctor asked and a worried look crept onto his face. "You don't mean time is ending? Because I've been through that before and I don't think I can handle that right now, what with Amy and Rory on their honeymoon and it would hardly seem fair to ask…"

"I meant," John said to stop the rattling. He hated it when people started to rattle. "I meant that it's Christmas, which means it's almost December the 31st."

The Doctor nodded. "Still, 2010... I'm way off! I thought I'd fixed her but she must have had a real knock on the head, from having been perpetually exploding for the full stretch of existence."

"What…," John started to say. Then he took a deep breath and added, "never mind." He let himself slump down until he was sitting on the pavement. Moreover, he officially gave up on understanding this conversation.

"Where - or rather when - did you think you were?" Sherlock asked. He was staring at the young man. Still not entirely sure why he felt the need to understand what was going on. Perhaps simply because it was a puzzle and he had spent his life solving puzzles.

"Oh, 2109," the Doctor said. "I wanted to visit an old friend."

"You are claiming to be a time traveller?" Sherlock asked. His voice neutral, but John knew what Sherlock must be thinking of this nutter in front of them. However, when Sherlock spoke again, John started to doubt his own convictions.

"So this box you've just gotten out of, presumably it's capable of close to light speed travel."

The Doctor grinned. "Humans, you never seize to amaze me with your simplicity." Sherlock gritted his teeth. Calling him 'stupid' was probably the worst insult you could use, when it came to Sherlock Holmes. "Time travel doesn't work like that. You could travel three times as fast as light and all that would happen is you'd be home for Christmas a lot faster. For time travel you need a vortex manipulator."

Sherlock gritted his teeth again. "Nothing can travel faster than light and when you get as near to that speed as you can, you will travel through time, not because you suddenly pop-up on the other side of a worm whole, but because time itself would move a lot slower for you than it would for everything not moving at the speed of light. Which is why travel to the past is impossible."

The Doctor chortled. "Travel to the past is not impossible, trust me." he smiled and pushed a hand through his hair. "In fact I've just come back from the 16th century, trying to patch things up with good old Bess… You think divorces are messy, well trust me you haven't seen messy until you've tried to divorce English royalty."

Sherlock let out a deep breath. "Time travel to the past is impossible because of the paradoxes that would unavoidably be created. And…"

"You tell Shakespeare that," the Doctor said, grinning again. He was leaning against his blue box now.

Sherlock gave the Doctor a look so full of contempt, it would've frightened most people.

"I've met him," the Doctor said, a wide smile flashing across his face. "And Agatha Christie, Charles Dickens - twice - and I already told you about Elizabeth. Queen Victoria, Churchill, Liz 10. Oh wait, that's in your future… Vincent… Van Gogh, I mean." The Doctor was counting them all off on his hand and all the while Sherlock felt his frustration growing. Somehow, he felt the need to win this argument, even though the man before him was clearly clinically insane.

"Oh and I've seen Pompeii burn, caused the creation of Torchwood, spoken to some Romans - well they weren't real but I didn't know that at the time."

"And you've done all that travelling in that police box?" Sherlock asked.

"You seem surprised," the Doctor said.

"Standing room only?" Sherlock asked and this was the first time he let his disbelief creep into his voice.

Fan boy, was the conclusion he came to. This was most likely a student and most likely, he had a star trek costume in his closet.

The Doctor smiled widely. "Perhaps it's bigger on the inside." His eyes grew wide for a second. Then he pulled open the door and went back inside the blue box, and then he stuck out his head again. "Listen to this," he said.

"Hello," he shouted into the empty blue box and it echoed. The hello echoed through what seemed like infinite space, though Sherlock could clearly see how small that box was.

"No object can contain within itself a mass greater than itself," Sherlock simply stated.

The Doctor simply smiled and shouted 'hello' into the empty space again. There was that echo again.

John, who had been getting wearier as the conversation had gone on and on, was now engaged again. He jumped to his feet and moved towards the open door of the blue box. His head disappeared behind the door.

Sherlock could hear John's gasp. John straightened himself and took a step back from the blue box. He looked at it from top to bottom, and then ran a quick circle around it. Then touched it, carefully as if expecting it to react to his touch. Then he disappeared into the blue box. The Doctor grinned at Sherlock and then disappeared into the blue box as well.

Sherlock was a little surprised John could even stand being in such a small space with the Doctor. Judging by the box's size, they must now be pushed up against each other.

Helloooo helloo hello…

Sherlock heard the echo again. It was the Doctor's voice.

Helloooooooo helloooooo hellooo helloo hello…

Then John's voice.

John jumped out of the blue box. "Sherlock, it's…" and he started to laugh. "It really is…" and he started to laugh even more, until he had to put his hands on his knees to keep from falling over.

The Doctor got out of the blue box as well. "You don't believe in time travel and you don't believe in an object being bigger on the inside than the outside?" The Doctor asked Sherlock.

"It is not a question of believe. There simply are certain rules that govern our universe," Sherlock said to the Doctor. Then he turned to John. "You were the one so set on me knowing about them."

John was still laughing. "I was wrong Sherlock."

"And if I can proof to you one of these impossible things, will you at least consider the other?" The Doctor asked Sherlock.

Sherlock clenched his jaw. "Alright, but you might find me a hard person to convince."

The Doctor sniggered. "I'm sure you are," he said. He pulled open the door of the blue box and held it open for Sherlock.

Hesitantly, but certain he was right, Sherlock walked through the open door. As soon as he entered the infinite space of the Tardis, he knew he had lost the argument.