The door opened to the hunched-over figure of Sherlock Holmes, his partner, John Watson, watching longingly from the sidelines. A stranger would presume the latter to simply want to be part of the thoughts running through the great detective's head, to be able to assist someone as clever as he. But someone like Molly Hooper could see the truth in the doctor's eyes and the way he rubbed his face tiredly that his desire ran deeper than work. The man beside her was oblivious to either of these things.

"Um, hello…" Molly started timidly.

Sherlock did not glance up from his work, but answered instead with a non-committal grunt. John glanced over, a swift smile beginning to form, on his lips. However, when he saw the extra person at the door he frowned slightly.

"Sherlock."

"Mm?" came the reply, uninterested.

"There's someone new."

If one thing could be said about Doctor John Watson it was that even after such a short time with his roommate, he knew how to get his attention. Sherlock finally looked up from his work, quickly appraising the new arrival. Then something happened that no one, not even the great detective himself could have foreseen.

Sherlock Holmes froze.

An awkward silence followed, broken by a little cough from Molly's direction, followed by an introduction.

"Well, um, this is Sherlock Holmes and John Watson, obviously," she attempted a small smile at this point, "And Sherlock, this is John Smith."

The newcomer stepped forward, speaking for the first time. "Actually, no, that not right, sorry Molly for the inconvenience, but that's not my name. I'm the Doctor."

"But that's impossible." Came Sherlock's voice, the smallest the room had heard it before.

"Not impossible," the Doctor grinned, "Just a little bit unlikely. Now, I heard you were good but this is fantastic!"

"What? What's wrong? Sherlock, what is it?" John pitched in with his usual tact.

"Molly, please leave."

"But … I …"

"Go."

Molly did as she was bid and Sherlock continued.

"John, you know everything I told you about aliens and the supernatural?"

"You said it was made up by the unimaginative and the dull."

"Yes, well, forget all of that right now, I've changed my mind."

"What?" John raised his eyebrows.

"Yes, my mind, changed, I've changed it, fvoom, gone, and new idea takes its place. Happens all the time, I'm just too clever for you to realise it."

"Yes, but … but why?"

At this point the Doctor stepped forward, "Ah, yes that would be me. You're a doctor aren't you? I love doctors. I'm called the Doctor, have I mentioned?"

"Ah, yes, yeah." John shook his hand. "Yes, so you said, but … who are you?"

He sucked in a breath through his teeth, "Well, that's the question, isn't it? But at this point I hand it over to Mr Sherlock Holmes, take it away Sherlock!"

Sherlock glared, and then sighed. "This man is impossibility personified, no matter how you wish to put it. He is, it seems, not of this world. And don't – " he looked over at John "- interrupt me. His clothes give it away. They completely mismatch, different sizes, different brands but they all compliment him. Stolen, but selectively. He has a sense of fashion, quite rare in thieves, don't you think? They take what they can get when they can get it, they don't … accessorise.

"Which brings us on to the bowtie, slightly too small for his frame, with multiple creases. He re-ties it often, sometimes not successfully, so he hasn't worn it too often before. But the creases also have traces of dust; he doesn't clean it frequently, giving us a clue of where he's been, which is where it gets tricky.

"This … dust. I cannot identify it, and I'm quite certain that if I had scans run on it, it would give me no further insight. Then there's the slight bulge in his jacket pocket, but … no, not a gun. A screwdriver, but again not of this world. I can smell it, in the air, even as we stand here. There's a whole list, but if I am correct, which I don't think at this point I cannot be, this … Doctor, is an alien. Which, as I was saying earlier, is pretty hard for me to accept, but true nonetheless. Am I right?"

The Doctor laughed merrily. "Brilliant! Oh, you're good you are, way beyond your time, though I can hardly speak. And you're quite right about the screwdriver too. Here –" he chucked a strange green tool at Sherlock, "-check her out."

Faced with something new, Sherlock relaxed a bit. He examined it as the other man explained.

"It's a sonic screwdriver; it literally opens doors for me."

"It emits a series of particles in a sonic wave," the detective speculated, "linked to another object of yours, but larger, it can't be on you at all times so you have this. You said it opens doors, so logically it would also seal them for you. But that's not it – if I just …"

He flicked the screwdriver so a claw-like attachment sprang out.

"It could do more. I'm presuming it can interact with technology, since any form of wave can interact with another, and perhaps … given enough time –"

"-it could resonate through concrete." The Doctor smiled. "Oh, I like you."

"So," John piped up for the first time in ages. "He's – you're an alien."

"Time Lord, actually." The Doctor replied, "I have a time machine."

"No." Sherlock raised his eyebrows. "How does that work, then?"

"Um, ah … wibbly-wobbly … timey-wimey …"

He took his screwdriver back and smiled.

"Do you want to see?"