"Yes, hello. Are the boys here?"
John was taken aback at the strange question, "Sorry, what?"
The man glanced inside and saw Castiel and walked right past John, his smile growing wider, "Ah! You look much better now!" He took his hand and shook it enthusiastically.
"Now wait a minute!" John said raising his voice, "Who are you?"
"Oh yes, sorry, sometimes I get so excited I forget to introduce myself. I am the Doctor." He extended his hand to John, who gave him a puzzled look, "Doctor Who?"
The man's face briefly lit up at the often asked question, it was always welcome. "Just the Doctor. Now!" He spun on his heels towards Dean and Cas and paused. "Where's your brother? He might want in on this conversation." Dean walked over to the chair Sam was sleeping and smacked his face, "Wake up, man!" Sam gave a surprised sound as he shook his head and saw Castiel standing upright. "Oh hey, Cas," His eyes stopped at the weird looking man standing next to him.
"I'm the Doctor, before you ask. Now, since everyone's awake, I bring you answers to your questions." When he was convinced that he had everyone's attention, he began, "I'm the one who brought you here." He held his hand up before anyone could interrupt him. "My scanner had picked up readings of something traveling through time and space and I found your friend here, looking quite exhausted, like he was going to drop out any second." He gestured at Castiel. "So I figured I brought you boys where I was sure you'd be safe."
"In London?" Sam asked.
"Yes, it's kind of a habit to come back here. Anyway! I also know what creature your after. The one with the upper body of a woman and the rest of her like a spider?" Dean and Sam gave each other a look and then back at the Doctor with the question "how?" on their faces. The Doctor nodded at them, "Yes, I'm hunting the same thing. It's an alien from the planet, Toolu."
"Wait, what? Aliens? Seriously?" Dean asked, taking a step towards the Doctor, "Aliens don't exist, buddy."
The Doctor's face darkened, "You know of things that most other people would deny, why stop at aliens? Everything that you've ever heard about, everything you ever feared in the dark, every little story you were ever told, exists. No one would believe you if you told them your friend, Castiel, is an angel, why won't you believe me if I said the creature you're hunting is an alien?" He stepped in closer to Dean, "Because even if you knew everything that you ever encountered is real, you still can't believe in anything else that you haven't seen, yet. Typical human behavior." The words of the last sentence was hammered out in a way that made Dean feel small.
An uncomfortable silence filled the room with the sudden tension. Dean was looking into the Doctor's eyes and finally nodded in apology. The Doctor then clapped his hands together, "Well then!" He said in a much lighter tone, "This alien, is on a mission. It's looking for something inside the void, outside the walls of reality.
"Do you know what it is?" Sam asked.
"I don't know yet, but if it's in the void, it must be something impossibly old and impossibly powerful, too powerful to even be allowed to exist here on this plane of reality."
"What's in the void, anyway?"
The Doctor gave him a look, "It's the space between realities. Between alternate universes."
"And what do you mean by alternate universes?" John asked, his interest piqued.
"I mean, other worlds like ours, only made different by the choices we make." The Doctor explained, "In this world we turn left, but then in another world you turned right. There are countless possible realities."
"And you're saying that it's possible to live in the space between these 'realities?'" Dean asked.
The Doctor paused a moment, "I wouldn't say living, no. More like... just existing. It's the place where time doesn't move at all, and the space is both small and vast at the same time. The point is, she's after something in the void. Something that slipped unnoticed through every imagination."
Dean and Sam tried to picture whatever this thing could be. Something that no one has ever created or even dreamed of. Something that isn't supposed to exist on their plane of reality. Even Castiel found it impossible to imagine something of the like.
"Fascinating."