Amelia Pond swung back and forth, back and forth, on the old decrepit swing. It was her eighth birthday, and she'd gotten her presents that morning. A bicycle from her Aunt, some My Little Ponies from Rory (typical – probably the last thing on earth she wanted. She wouldn't tell him that though) and Mel's sizeable collection of drawings of the Doctor. They weren't completely accurate; after all, Mel hadn't actually met him. But Mel was a good drawer, far better than Amelia, and she'd always envied the girl's ability.

It hadn't been a bad birthday. But Mel and Rory had gone home now, and her Aunt had left for the pub – again. And now Amelia was sitting in the local park, swinging on the swing all by herself, and wiping away the tears that she couldn't stop from falling.

It wasn't like she'd expected him to come on her birthday, she told herself, although she knew it was a lie. He was just as likely to show up out of the blue on any other day of the year.

But she'd had a good feeling about today. A good feeling that had disappointed her again.

"Stupid, stupid, stupid, stupid," she said, although she wasn't sure whether she was talking about herself for hoping, or him for disappointing her.

"Don't beat yourself up about it," a deep voice said from behind her. "Most people are."

She whirled around, almost falling ungracefully off the swing. It was a lanky teenage boy with bright grey eyes and sharp, chiselled cheekbones. He was dressed well, with clothes that were in good condition but were not overly formal, and under one arm he carried a thick folder. "Who're you?" she asked suspiciously.

"Never you mind," the boy answered. "The question is who the Doctor is?" He emphasised the words the Doctor, for no apparent reason. Then he sat down, cross-legged, in front of Amelia's swing and began arranging pieces of paper.

If Amelia hadn't been suspicious before, she was now. "How do you know who the Doctor is?" she asked.

The boy shrugged. "A combination of crime reports, history books, and illegal access to government files through my brother's new job," he said, bored, as though the question was of no importance. "Now, where were we? Are you Amelia Jessica Pond?"

"Yeeees," she said cautiously, drawing it out. "Why do you want to know?"

He looked up sharply from the pieces of paper he was arranging before him. "Because you have an imaginary friend called the Raggedy Doctor, who you told your psychiatrists wears a bowtie and travels around in a blue box. You also say he's coming back for you."

"They don't believe me," Amelia said bitterly, her suspicion forgotten in favour of complaining about her psychiatrists. "They say he's not real."

"They're idiots," the boy said sharply. "Everyone is. The Doctor is real. He travels through space and time, and his name keeps popping up all over the place. He was in Pompeii." He paused to pull out an image of a Roman statue with a man, a girl, and a phone box. "He was in Victorian England-" He shuffles through and finds a photo of an Elizabethan painting. "And he's been photographed hundreds of times this century."

And from his stack of papers emerged a large amount of photographs. "I have more at home," he said, and Amelia thought she heard a distinct note of pride in his tone.

"They're all pictures of different people," she pointed out, hoping to wipe that self-confident smirk off his face.

If anything, his grin got bigger. "His face changes," the boy said. "I haven't quite worked it out yet. But it's like there are several doctors, all appearing throughout time. I think it may be some sort of secret order, although that doesn't explain how the same face can be in the first century and the twenty-first century."

"You're wrong," Amelia informed him. "It's not an order."

"Isn't it?" The boy didn't sound angry or annoyed about being wrong, merely… intrigued.

"Nope. He's an alien. He travels in time and space in his blue box. That blue box," she said, pointing at a picture of the TARDIS.

"Really…?" the boy said, more to himself than to Amelia. He didn't immediately discount it, although he didn't sound like he believed her either.

"Yes," Amelia said. "He's coming back for me. He's going to take me with him."

"Is he now?" the boy said. It wasn't mocking or patronising, like some of her psychiatrists had been. It was more like he had something else on his mind.

"That's my Doctor," she said, pointing to a photograph of a man wearing a bowtie.

"I know," he replied. "I have plenty of pictures of him. It's the other 'him's I have trouble with. I've spent hours recovering almost-wiped files – something called a Bad Wolf virus. I think the name's a clue."

Most of this went way over Amelia's head. But she did pick one thing up. "So you're looking for him too?" she asked.

"Yes I am," the boy told her, beginning to scoop up his papers.

"Well if you find him, can you please tell him Amelia wants him to know that he's late," she said demandingly, emphasising the late part.

He looked at her with sombre eyes for a moment. "Indeed I will, Amelia Pond. Indeed I will."

Then he scooped up his file and stood up, walking briskly towards the park gates. "Wait!" Amelia called. "You never told me your name!"

The boy turned to her, assessing her silently. Finally, he flicked his dark-blue scarf further over his shoulder. "Holmes," he said, as though she should be impressed. "Sherlock Holmes." And then he turned on his heel and marched out of the park.

Amy pondered that meeting for about a week, before promptly forgetting about it for the next fifteen years. Forgetting, that is, until he found her again – her, and her Raggedy Doctor.

The first thing Sherlock said when he met the Doctor was not what anyone expected.

"Wrong," was the first word he said to the strange man.

The man in the bowtie looked up, surprised, from where he was talking animatedly to Lestrade. "I'm sorry?" the Doctor said, looking slightly puzzled,

"Wrong," Sherlock repeated. "Your name isn't John Smith, you're not a secret agent from MI7 here to inspect this dead body, and that form of identification you're holding isn't an agent's badge."

"Yes it is," the Doctor said, after a moment's hesitation in an attempt to bluff his way through this.

"What are you talking about, Sherlock?" Lestrade said. "The man is clearly from MI7. It's got all his details on his badge, and I think I'd recognise a fake when I saw one."

"It's not a fake," Sherlock said, standing up and stepping away from the body. He gestured for John, who was watching on with obvious curiosity, to take his turn examining the body. For once, the good doctor was reluctant to do so – this verbal rally Sherlock had engaged in looked far more amusing. John was interested to see where it might lead.

"Then if it isn't a fake," Lestrade said through gritted teeth, "he's from MI7, and therefore everything he just said is correct after all."

"Wrong," Sherlock said again, in that same bored voice. "It's not a fake, it's psychic paper. He wants you to see some form of identification that will allow him to view the body and discover that there is, in fact, tiny puncture marks below the left ear. He chose a well-known government agency with more authority than the police and would be likely to have interest in a dead body. Therefore, MI7. Although he didn't know what an MI7 badge looks like enough for the psychic paper to mimic it, it's psychic field managed to tap into your knowledge of what a badge would look like. The only faults that badge has are ones that both you and he do not know about."

Lestrade was gawping at Sherlock openly. Even John was looking a little startled. Sherlock dealt in facts and figures; psychic paper sounded like something that came out of a science fiction book or a secret agent film. Had the eccentric detective finally gone around the twist?

Then something surprising happened. The man in the bowtie threw his head back and laughed. Lestrade and John looked at him as though he'd lost his mind.

"What's going on, Sherlock?" John asked warily. He felt that something strange was happening. And not the usual-strange; this strange seemed like something completely different.

"His name's the Doctor," Sherlock informed him. "Doctor, this is DI Lestrade and Doctor John Watson."

"Pleased to meet you," the Doctor said, beaming.

"The Doctor?" Lestrade asked. "Doctor who?"

"Just the Doctor."

"You can't call someone, 'the Doctor'. That implies there's only one doctor, and he's it. And I know for a fact that John would object to that."

John, who was still crouched over the dead body, looked too fascinated by what was going on to object to anything. "Is he the one you were going on about, Sherlock?" John asked. "Is he one of the three men who have been able to outwit you?"

Sherlock pursed his lips. "It's not that he outwitted me," he said carefully. "It's that I couldn't find him."

"Sounds like outwitting to me," John said, straightening up.

"He was jumping time tracks all over the place," Sherlock argued. "How are you supposed to find someone who won't stick to one era? You'd need years to locate them, and I lost interest."

While Lestrade and John were puzzling over whether Sherlock had actually lost his marbles or not, the Doctor took this opportunity to interrupt. "Actually," he said, "Someone found me in something like twelve hours once."

"Really?" Sherlock said, apparently fascinated. "Did they have a time machine, or something that locked onto the huon energy of your TARDIS?"

"Neither," the Doctor said proudly. "They had a bus and a twelve-person army of senior citizens."

"Fascinating," Sherlock said, steeping his fingers together. "And-"

But Lestrade cut him off. "This is all very well and good," he said somewhat snappishly, "but we have a dead body lying here and a murderer quite possibly running around the streets of London-"

"Wrong," Sherlock said again. "The murderer's dead. She was a creature called a herbisecotr, an alien who takes human form in order to mingle among us and lay eggs inside a human. The eggs then incubate for a period of months while the dead body rots, before escaping out, breaking out of the coffin, and repeating the cycle all over again. The herbisecotr only breeds once, after which it tends to crawl into the sewers and die. As long as this body is incinerated, Detective, you have nothing to worry about."

Lestrade was gawping again, and he wasn't the only one. John was looking very concerned about Sherlock, and even the Doctor appeared mildly surprised. "I imagine that usually Torchwood cleans messes like this up," Sherlock commented, "but ever since the Wales and London section fell, aliens like this-"

"What do you mean, Wales fell?" the Doctor interrupted.

"What? Oh, they got blown up a while ago," Sherlock answered carelessly.

"All of them?" the Doctor asked.

"Two survived."

"Jack?"

"Still breathing. Although I don't see why he does it; he's the only person on this planet who can get away with not doing it. It's so boring."

"Thank goodness," the Doctor replied, ignoring the second part to Sherlock's answer.

"You're a bit behind, aren't you?" Sherlock asked. "That happened ages ago."

"Not meaning to interrupt," Lestrade interjected angrily, in a way that meant interruption was clearly his intent. "But for those of us who aren't familiar with Torchwoods and aliens and stuff…."

He said the word 'aliens' like he wasn't quite convinced. John didn't blame him; he was the man who regularly followed Sherlock into life-threatening situations just for kicks, and even he was struggling with this one.

"And that'll be Amy!" Sherlock exclaimed, as a girl with flaming hair strode towards them, a blonde man walking behind her. "Long time, no see." Then he turned to the Doctor. "She wanted me to tell you that you're late, by the way."