A.N: This will eventually be a Supernatural/Doctor Who/Sherlock (if you haven't seen Sherlock, stop now and go watch it, it's amazing) crossover. I'm trying to keep everything as close to canon as possible, but there might be various hints at random pairings, but nothing one can't ignore.


Chapter One

Convergence

The TARDIS's phone was ringing, and the Doctor almost missed it; he had been on his way out and only caught the sound just before he closed the door behind him. Looking out at the stunning blues and pinks of a strange new planet, he sighed and turned back to his TARDIS, knowing that the call might very well take him away from this almost-adventure, but what was the point of having a phone if you just let people wait impatiently on the other end? He had to answer it.

"Hello," he said cheerfully, wondering who would be on the other line. He hoped not Marilyn; she was still upset about that whole wedding misunderstanding.

"Doctor!" came a fondly familiar voice, and he couldn't help but smile.

"Amy Pond, good to talk to you. What's happened? Not more Cybermen, I hope—" He'd given them his number in case they needed him for some world-ending emergency, or to invite him to another Christmas dinner.

She cut him off, "Oh, no nothing like that. It's just, well, it's our anniversary, Rory's and mine, and we were wondering if you could take us to a nice peaceful location, without any other people around, maybe sometime a few million years ago? But not far enough back for the dinosaurs because that doesn't sound relaxing at all. Lately we've felt like we can't get half a moment to ourselves."

The Doctor was silent for a moment. They wanted to travel with him again, even after all he'd put them through.

"I promise this is just a one-time trip, to a nice empty beach," Amy continued, as if reading his thoughts, "On Earth. No aliens, no life-threatening situations, just a nice vacation."

"Oh, alright," he replied at last, his smile turning into a wide grin. "I'll be right over. Prepare for the best anniversary trip in the universe!"

They said their brief goodbyes and the Doctor hung up, typing in the space/time coordinates of Amy and Rory's house.

About a minute later, he landed. "Alright, Sexy," he said, "We're having company, but don't be jealous—you're the only girl for me. But don't tell River i said that, you know what it does to her." Trailing his fingers briefly over the controls, he turned and dashed out into the street, expecting to see the Ponds' cute little house.

Instead he saw a dark alley, and it wasn't a particularly clean one, either. This wasn't a residential neighborhood, and by its smell, it wasn't even in England. He looked at his watch. He was in the right time, but the wrong place.

Frowning, he began to turn back towards the TARDIS's door, wondering why Sexy had missed so badly, but flickering streetlamps paused his steps.

Well, now, trouble. Wasn't as if he could walk away from that.

Dean didn't notice the newspaper in front of him for a few seconds after Sam had tossed it there, but eventually he made his eyes drag across the headline. Dozens of missing people. Huh. He sipped his glass of whiskey apathetically.

"Well?" Sam asked impatiently, "What do you think? Sounds like our kinda job."

"Probably, yeah. Guess you wanna go check it out."

"Don't you? We've been getting nowhere with the Leviathan, so maybe a regular job is what we need to get out of this slump."

Dean was finding it difficult to muster the wherewithal to care. He'd hardly slept the night before because of the dreams—in them he watched Castiel die over and over—and his exhaustion went deeper than mere physical tiredness. Everyone he cared about was gone except Sam.

And now Sam wanted him to give a shit about some missing people in—he glanced back at the newspaper—Atlanta. But there was nothing else to do, really. Dean rubbed his eyes and nodded. "Yeah, let's get packed, long drive."

The following night they arrived in Atlanta and checked into a cheap motel on the edge of town. Sam began planning a course of investigation immediately, and Dean pretended to listen to him.

"The people all disappeared from a relatively safe area, Midtown. I mean, Atlanta has a high crime rate, but these disappearances are different. I'm thinking something with teeth and claws is pigging out here."

"Mmhm," Dean murmured, staring at the wall, wondering if he should bother trying to sleep.

"It's too late to head out now, but I think we should get an early start. I was thinking FBI, but they might already be here, and we don't—"

Dean glanced up at his brother, whose expression was pained though he was obviously trying to hide it; Sam's right hand was holding his left palm, knuckles white. "We don't have Bobby. Yeah. So what do you think? Reporters?"

"Maybe."

"I think we should go now, take a look around."

"It's 2 AM, Dean."

The older man shrugged. "We don't have to go into any buildings, right? I know I won't be able to sleep, so let's just get this over with."

They drove to Midtown and parked a block down from the area where most of the people had gone missing. Armed with just about every weapon they knew would hurt various monsters and spirits (including industrial soap), the brothers began to move slowly down the street, looking for signs of anything.

"No EMF so far," Sam whispered, "And I don't see any sulfur."

"That narrows it down." Dean rolled his eyes. He was about to make some comment about the uselessness of their investigation and that they should just go get drunk or something, but a voice floated out of a nearby alley, stopping him.

"Oh, hello there, little girl," said a man in a British accent, "What are you doing here this late? Shouldn't you be in bed?"

"My boss sent me to work. I think he's mean," replied a sweet, childish voice. "I'd rather eat than work."

"Well," the man answered, "how about I take you home so you can get something to eat?"

Sam and Dean were almost to the mouth of the alley, and the latter had a definite bad feeling about who or what that little girl was. They both wordlessly raised their shotguns and peaked around the wall.

The girl had white-blond hair and was wearing a baby-blue dress; the Winchesters arrived just in time to see her turn into a monstrous thing and pounce at the man. Without hesitation, Dean fired, hitting the girl—the demon. She screamed and turned on them, then paused.

"Oh, no," she said petulantly, "It's you! You're ruining all my fun!" And with that, she burst into a cloud of black smoke and rushed away.

"You okay, buddy?" Dean asked, walking towards the man, seeing him for the first time. He was young and had a sort of hipster look about him—bow-tie and suspenders. But at least he didn't seem to be bleeding.

"You shot her!" the man said, "Well, I assume it was a her. What was that?" He gave a mean frown to the weapons in the hunters' hands, then glanced back up at them.

"A demon," Sam answered, "She wasn't a little girl, only disguised as one. She would have killed you."

"A demon?" the man was smiling suddenly, "That's marvelous. Where am I?"

"Uh," Dean exchanged a look with his brother. "Midtown. Atlanta."

"Ah, the Deep South," his smile briefly faltered into a grimace. "Haven't been here in a while. Well, thanks for helping me. I'm the Doctor, by the way. Who are you?"

"I'm Dean Winchester, this is my brother, Sam," he found himself saying before he could stop, which shocked him. Giving their real names to a stranger was completely idiotic considering their recent infamy.

"Nice to meet you, Dean, Sam." He looked around. "Did this demon cause the flickering lights?"

"Uh, yeah," Sam responded. "I'm sorry, you're the…Doctor? Doctor who?"

"Just the Doctor. Well, I'd better be on my way."

"Wait—it's still dangerous out there. Something's been taking people, and it wasn't the demon." Judging by what the demon had said about working for a boss who didn't want the Winchesters bothered, she'd probably been sent here by Crowley, which meant the demons had no idea what was happening, and that wasn't good.

"Taking people?" the man who was apparently called just Doctor turned slowly back around to face the hunters. "And you're positive the lights were a result of this demon? Absolutely sure?"

"Uh, yeah, like, maybe 95 percent," Dean answered, glancing at Sam, who shrugged his vague agreement. "Spirits usually cause electrical problems. Why?" He narrowed his eyes, "What else could it be? Do you know something about this?"

"No, I only just arrived. And I really need to be getting on," he threw a glance down the alley, and Dean followed his eyes, noticing at last the oddly placed blue telephone booth. It looked British, but he'd thought they were supposed to be red. "But I should stay long enough to be sure," the Doctor finished quietly, as if to himself. "Yes, alright!" Whirling around and pulling something from his breast pocket, the Doctor strolled past the Winchesters, moving towards the street. "Is this the area where the people disappeared?"

A strange, warbling noise almost interrupted Dean's answer in the affirmative.

"What's that thing?" Sam asked before his brother got the chance.

"Just a screwdriver," the Doctor answered dismissively, pointing the thing in random directions.

"Why is it glowing and making noise, then? And what screws are you attempting to drive?"

The Doctor gave Dean an annoyed frown. "It's a Sonic Screwdriver, and it does more than screws. It does everything. Except wood."

"Yeah," Sam said, his tone clearly conveying just how insane he thought this bow-tie-wearing man was.

"Something is very wrong here," the Doctor continued, ignoring Sam, "There's a thinness here that shouldn't be. This isn't the site of a rift. So these things you call demons," he turned back to the other men, "They're some sort of alien?"

The Winchesters broke into simultaneous peals of laughter that echoed inappropriately off the dark alley walls.

"Aliens don't exist, dude. Those demons are real demons. You know, from Hell."

The Doctor stared at them seriously. "You don't remember a few years back when the Daleks stole the planet? Whole new sky…? Were you lot asleep the whole time?"

"What's a Dalek?" they both asked, voices in perfect unison.

"No," the Doctor said incredulously, raising his screwdriver and pointing it first at Dean, then at Sam. Both of them tensed up, neither sure it wasn't a weapon, but nothing happened but that strange, warbling noise. The Sonic Screwdriver popped up and the odd man looked at it, gasping. "No! This isn't possible. Nothing about this can possibly be evenly slightly possible."

"Hey," Dean asked irrelevantly, "If that's a Sonic Screwdriver, why does it have the light? That just for show, or?"

The Doctor rolled his eyes. "You humans, never focusing on what's important."

Humans. The man—no, not a man—said it in a way the made Dean certain the Doctor wasn't human. Both the hunters raised their guns, aiming for the stranger.

"What are you?" Dean spat.

"I," the Doctor answered quietly, his hands raised but not appearing afraid, "am not someone you want to point those things at. You believe in demons and spirits, but not aliens?"

They nodded.

"Well, then, you need to open your minds. I'm an alien. But I'm not just from another planet. I'm from another universe entirely, and I've landed here by an impossible mistake."

"If it was impossible, how did it happen?" Sam asked, a little snarkily.

"I can't very well figure that out if you two stand here all night threatening me. I'm not human, no, but why does that mean I want to hurt you? Or anyone? I'm just here to help."

"Why do you look human? Did you steal that body?" Dean held his gun steady but was having doubts about his original opinion of the Doctor. He seemed sincere, and that made the hunter want to trust him.

"Steal it? No, this is just how I look. I'm a Time Lord. You lot look like us, but there are differences. I have two hearts. If you'll let me," he began to slip a hand into his pocket, then slowly withdrew a stethoscope, "I can prove this body isn't human. Listen to my hearts." He tossed it to Sam who caught it easily.

Though his younger brother didn't need telling to be cautious, Dean said it anyway. Rolling his eyes back at his brother, Sam lowered his gun and raised the stethoscope to the supposed-alien's chest. After a moment, he let out a small gasp.

"It's true. Two heartbeats."

Dean reluctantly lowered his gun. He'd never heard of anything with more than one heart, so the Doctor could be on the level. Something about the man seemed honest and straight-forward, but Dean wasn't prone to trusting strangers easily.

The Doctor lowered his hands and took the stethoscope back from Sam. "Well, now that no one's threatening me anymore, I can try to find out how I got here. It wasn't through a crack in the time vortex, or I would have felt it. So how?" The last words were clearly spoken to himself, and he once again turned and began to point his Sonic Screwdriver in random directions.

A few moments later, the warbling sound rose in pitch until it was almost unbearable to the Winchesters. Dean covered his ears with his hands, so he only saw the Doctor's lips move, forming frantic words, and then the two-hearted being dashed off down the alley, motioning for the brothers to follow. The expression on the Doctor's face—fear—made him take his hands from his ears and shout, "What? Where are you going? What's happening?"

The high-pitched noise was gone now, so he and Sam could hear the Doctor when he replied almost frantically, "Run!"

But the Winchesters didn't move; they weren't about to follow a strange creature further down a dark alley—Dean still wasn't sure this so-called Time Lord wasn't involved in the disappearances.

Before he could make a decision on whether or not to follow the Doctor, the world around him shifted in some way that he couldn't exactly perceive with his usual senses. Dean suddenly knew that something was terribly wrong with his surroundings, and he was sure, for a millisecond, that what had happened to the missing people was about to happen to him and Sam.

Closing his eyes and drawing in a slow breath, adrenaline stretching time out as it will, Dean decided he should have gone after the Doctor. The lids of his eyes slid open again; he would not face whatever was coming with his eyes closed.

What he saw was more shocking than anything he had imagined. A dark, off-the-rack suit, a loose blue tie that was almost inexplicably twisted and disheveled, a shadow of a beard, tousled black hair—Dean saw all this in an instant, but his vision settled on those blue eyes, and he said, feeling at once a mixture of relief, hope, sorrow, and despair that was so powerful and confusing that he could hardly make heads or tails of his emotions, "Cas."

Dean thought he heard Sam say something similar beside him, and then the angel was touching both of them on the forehead, and they were at the end of the alley, next to that weird blue telephone booth. The Doctor opened the door with a key, shouting something—Dean wasn't sure what, but he knew it didn't matter—and Castiel pushed the Winchesters inside.

The Doctor closed the door behind them and sighed, leaning up against it. "Well, that was close, wasn't it? You boys should learn to run when I tell you to run. Cardio is very important." He smiled. "Who's your friend?"

Dean didn't answer; it all made sense now. He was dreaming again. Each night was a toss-up between having nightmares in which he witnessed the people he loved dying again and again or dreams in which his friends and family were still alive. He often dreamed that Cas was still with them, always there when he called, always willing to help. Those nights were worse than the ones filled with horrors; waking from a nightmare was a relief, but waking from a wonderful dream to an empty, grey world was soul-crushing after a while.

This was a pretty messed-up dream, what with the aliens and all, but Dean assumed he was in the Impala, Sam driving them ever closer to the case in Atlanta. He'd just fallen asleep wondering what could be taking the people, and now his subconscious was playing out this bizarre, nonsensical scenario in hopes of figuring something out. Sometimes dreams could be useful, but this one was a bust.

Still, he might as well go along with it.

There was a long silence after the Doctor's question; the Winchesters were staring at Cas, and the angel was avoiding meeting their eyes now, his expression a little embarrassed and almost ashamed—and he looked so strange without his trench coat, like he was too small. Eventually Cas answered himself, saying, "My name is Castiel, and I was sent here to help you."

"Help me?" the Doctor asked quietly. "Help me with what? And who sent you?"

"I don't know with what, but God sent me."

The two-hearted man's mouth twitched up in an almost-smile as he said, "God? Like, the God?"

"Yes," Cas's voice had an unmistakable edge of an added, "Problem?" as he spoke. "And he sent me here just in time." Turning to look at the Winchesters at last, he continued, "I know you sensed something happening back there. I can only assume I am meant to help this man discover what it was."

Dean frowned, not because of what Cas was saying, but because by this point, when he realized he was dreaming, he usually began to slip into consciousness, especially if he was sleeping in the Impala while Sam was driving. But everything still seem solid, vivid.

For a single moment he allowed himself hope, but he crushed it ruthlessly. This wasn't real, it couldn't be. Cas was gone, and he certainly wasn't standing inside a blue booth with an alien—

Glancing around the room, Dean finally noticed the discrepancy in the size of the interior of the phone booth. "Uh," he interrupted, "Where the hell are we? This place—it's bigger on the inside."

"Yes!" The Doctor's voice was bright, "Welcome to the TARDIS. That's T-A-R-D-I-S, stands for—"

"But, wait, is this your alien spaceship or something?" Sam asked.

"Time and relative dimensions in space," the Doctor finished, "And yes, it's my ship. It does time and space. Best in the universe. So, Castiel, some entity sent you to help me. That means this is big. Dangerous." He was grinning. "And it's impossible, of course. I love impossible." Eyes darting from face to face in the room—which looked to Dean like something off the set of a cheesy sci-fi movie, full of useless knobs and crazily designed gadgets—something changed in the Doctor's expression, and he quipped, "Sam, I need your help. We have to figure out what's going on, and for that I'll need to know what brought me here. I think it might have to do with you and your brother."

"Okay," Sam nodded, looking dubious, but he followed the man to the other side of the room, where the Doctor began to speak quietly to him and wave that Sonic Screwdriver thing around. Even from that distance, Dean noticed that his brother was pressing the center of his palm; Dean didn't blame him for doubting what was real.

Oddly accurate dream he was having. Very realistic, if you looked beyond the aliens.

"Dean," Cas's voice brought the hunter back to Earth—relatively speaking. "I want to apologize again for what I did. I don't deserve forgiveness, but I promise I will never lie to you or conceal anything from you again."

This dream wasn't really like the others; usually everyone went along as if nothing had ever happened. Cas never apologized because in Dean's ideal world the angel had nothing to seek forgiveness for.

What if this is real? wondered a small voice in Dean's mind. What if he's really back?

"Cas, I want to forgive you. I want to let it go. But you let the Leviathan into the world. It's gonna take time for me to trust you again."

They both knew the Leviathan weren't the reason Dean was having trouble looking Castiel in the eyes. The hunter had trusted his friend completely—he'd had complete faith in the angel—and Cas betrayed them. The only reason Dean wasn't punching him in the mouth was that he knew he'd done it all with pure intentions. Cas had been trying to shoulder the responsibility of saving the world from becoming the battleground of some petty sibling feud.

Glancing around, Dean set his shotgun on the nearest available surface, beginning to surrender to the idea that he was awake and all this was real. Stranger things had happened to him, and an alien from an alternate reality wasn't impossible, as he and Sam knew well.

He turned back to face Cas, stepping towards the other and pulling him into an embrace. "I'm glad you're alive," he whispered, "I'm still pissed. But you're family." He released the angel and moved back quickly; the hug had been awkward, as if Castiel hadn't been sure what to do with himself—or perhaps he was just surprised.

"Thank you," the angel murmured. "And what I said before the Leviathan—" His eyes flickered down, and he swallowed, as if trying not to remember something painful, "I meant it. I will redeem myself."

A sudden beeping coming from the weird-looking consol in the middle of the room prevented Dean from answering, though he hadn't been sure of what to say, anyway. He was still sorting himself out, because Cas was back. This was real.

Across the room, the Doctor exclaimed, "Oh, well that's interesting! Dean, Castiel, come over here for a moment," he waved them towards him, eyes not leaving the screen he was looking at.

"So," the bow-tie-wearing man began as the other three stood beside him, peering at the screen. To Dean it looked like a bunch of random circles and other nonsense, but apparently the Doctor could read it. "I was asking myself how I could have gotten here to this universe, but I realized that wasn't the question that mattered—at least not at the moment. What's really important is how the TARDIS still has power. You see, she's draws the energy she uses from the universe, but it has to be my universe." He stepped away from the screen and began to pace, talking quickly and gesturing demonstratively.

"But obviously she still has power, which means the TARDIS is still connected to the universe I came from. But that's impossible, because I'm not in my universe."

"Maybe the doorway is still open?" Sam suggested.

The Doctor was shaking his head. "I didn't fall through a crack in the time vortex, or come through a doorway. There are no doorways."

"Bullshit," Dean interrupted, "We went to a parallel universe once," he grimaced, "It was weird, but it happened."

"You did?" the Doctor paused his pacing and took a pair of what appeared to be old-school 3D glasses out of his breast pocket. Putting them on and looking around the room, he laughed, "No, you can't have gone. There's no void residue on you."

The Winchesters were taken aback by the Time Lord's easy dismissal of their claims. "Uh, yeah, we did go. An angel sent us with some kinda spell," Dean insisted, a little annoyed.

"Angels?" The Doctor's voice was laced with mirth, "Angels and demons. What an interesting place I've landed. I hope these angels aren't as violent as that little demon I met."

"That would depend on which one of us you met," Cas replied seriously. "Some angels have no love for mortals."

"You're an angel?" He laughed, "Well, I better not blink then, eh?" Chuckling, he glanced around the room, as if waiting for everyone else to get his joke. "Ah, yes, that's right," he murmured, sounding almost sad, "Never mind. So you're an angel. No fluffy white wings?"

"This is just a vessel. I cannot be on this plane of existence in my true form."

"A vessel?" The Doctor pulled out his Screwdriver and aimed it at Cas, scanning him quickly then looking at whatever reading it displayed. "My, you're lucky people are bigger on the inside, or you wouldn't fit. So it's alright for him to use a human body as a host, but you were about to shoot me over the same thing?" He gave the Winchesters a disapproving glare. "Talk about double-standards"

"This body is not occupied by anyone else," Cas said, surprising everyone. "Jimmy Novak's soul is in paradise. This form was made for my use, I suppose so that you would recognize me."

The TARDIS beeped again, drawing everyone's attention back to it. The Doctor glanced at the screen, nodded, then resumed pacing. "As I was saying, I didn't come through a crack, because if I had, the TARDIS wouldn't be running at full capacity. The energy of the universe can't traverse the void."

"The void?" both Winchesters asked in unison.

"It's what separates all universes. It's the space between reality." Their expressions, or maybe just Dean's, must have prompted him to explain more fully what the hell he was talking about. "There are an infinite number of universes, each one arising from a different choice or action that was made. Some are similar to each other, some radically different."

Everyone else nodded during the short pause in the Doctor's explanation, even Castiel, who probably knew most or all of this already.

"In between them is the void, where there isn't time or space or anything. Imagine the universes like bubbles, and you have this huge group of bubbles all floating around but not touching."

"Okay." Dean nodded.

"It's nothing like that, really, but if the image helps." He shrugged. "To travel between universes, you have to go through the void. Only I didn't, somehow." Stopping mid-pace, the Doctor's eyes grew wide, and he whirled to face the hunters.

"You said something was taking people?"

They nodded, perplexed by the sudden change in topic.

"There isn't a rift here, the TARDIS would pick it up. Which means the people are slipping into another universe through other means, the same way I got here."

"Which is?" Sam asked impatiently.

"Impossible." The Doctor ran a hand through his already-disheveled hair. "But there's no other way."

Sitting down on a strange bench-like chair near the center consol, Dean said sarcastically, "Let us know when you wanna stop being so mysterious."

"I'll need to run more tests before I'm sure."

The knock on the door was so innocuous that at first no one seemed to notice, then it was repeated, a little more loudly, but still polite.

"What?" the Doctor said, giving the door a perplexed stare. Whoever was outside knocked again, and finally the owner of the ship—or whatever it was, time machine, weird blue magic phone booth—made his way to the entrance, opening the door slowly.

Dean was too far away to hear the exchange of words, but the Doctor seemed pleased about something, then confused. The hunter was distracted from eavesdropping by the sudden ringing of a telephone, though, which he saw on the consol. Thoughtlessly, he stood and picked it up, ignoring a look from his brother as he did so. Sam probably thought it was rude, but he wasn't about to sit around listening to an annoying ringing phone.

"Uh, hello?" he said, wondering what sort of person called a time machine at this hour of the night.

"Who is this?" demanded a woman's voice, her accent sounding British—no, Scottish, maybe, Dean corrected himself. Probably Scottish. "Where's the Doctor, and why is he letting random Americans answer the phone when he should be coming to pick up me and my husband? Well?"

"Whoa, calm down lady, I'm just, yeah the Doctor guy's here, but we're kinda dealing with a situation and—"

"Put the Doctor on, and tell him he's two hours late!"

Dean covered the receiver and called over to the door, "Hey, Doc, phone call, some chick who sounds pissed. Says you're late."

The Doctor had stepped out of the TARDIS, but he popped his head back in, frowning. "You answered my phone? Don't do that! And oh," he looked at his watch, "Tell her I'll call her back in a bit, and that I promise I won't be much longer!"

"He says he'll call ya back," Dean relayed the message cautiously; the woman on the other end of the line seemed fiery to say the least. "In just a few minutes."

"Tell him he better," she threatened, "And I'll be looking forward to meeting the man who the Doctor lets run around answering his phone when he snaps at his own mother-in-law for doing it." The line clicked dead after that.

Dean hung up slowly, wondering where the Doctor's wife was, if he had a mother-in-law. Or maybe she'd been joking. "That was weird," he commented to his brother, who was awkwardly loitering a few feet away, staring around the room.

"What part of this isn't weird?" Sam retorted, still pressing his palm almost desperately.

"Sam, Dean," the Doctor called, once again stepping back into the TARDIS, "You've got a friend out here who's looking for you!" His smile was almost infectious, and perhaps Dean himself would have grinned, but he knew he and Sam had no friends left outside that room, which meant trouble.

"Weird thing is," the Time Lord continued, "He looks like someone I used to know back in my universe. Weird how these things work out, isn't it?" As he said those last words, the Doctor's smile faded; he'd probably noticed the other three men's expressions.

Dean picked up the shotgun he'd set down earlier, and Sam did the same. Then the three wordlessly walked towards the door, even Cas's posture that of someone preparing for a fight.

"Why are you all so serious?" the Doctor asked nervously, "Is he not a friend?"

"Not likely," Dean replied, pushing open the door. Standing in the alley a few yards away was Crowley, looking bored and impatient.

"Oh, nice of you to finally come out and say hello," he rolled his eyes, "Just keep me waiting as long as you like. Not like I'm the king of Hell or anything."

"What do you want?" Cas asked, stepping out of the TARDIS behind Dean and Sam.

"Well, look who decided to come back to life. Where's that tan coat of yours? Finally decide to care about fashion?" Crowley began to meander towards them, but the Winchesters simultaneously raised their guns, and he stopped, lifting his hands up. "I'm just here to chat, not start a fight, so how about you put those things away?"

"Yeah, no," Sam replied. "What do you want to chat about?"

"Don't be daft. You know why I'm here. Something's going on, and I want to help you figure out what."

"Why?" Dean narrowed his eyes.

"Because nearly thirty people have gone missing here in the last two weeks. Things like that are bad for business, because those people didn't die, they were taken. And some of those souls belonged to me."

"Souls?" the Doctor said, joining the group in the alley, but standing next to the door, which he didn't allow to close all the way.

"Oh, he didn't mention? This guy runs Hell." Sam's expression was one of false mirth. "Great friend of ours."

"Somebody's got to be the bad guy," Crowley shrugged. "And I'm an improvement on Lucifer, or the Leviathan."

"Marginally less of a douchebag, still a douchebag."

"So you want to help?" the Doctor interrupted, "I have an idea about what could be happening, but it's impossible, so any other information you have about this—" He paused. "Wait a moment, Dean, what was the name of the woman who called me?"

"Uh, she didn't give a name. Some Scottish chick who was pretty forceful. Said she was your mother-in-law."

"That was definitely Amy," he muttered to himself, "which means…" Letting his sentence trail off, the Doctor spun back to his TARDIS and ran inside. After a few seconds, everyone in the alley followed, even Crowley, despite the Winchesters' collective mean glare.

The elder brother noticed Cas wasn't taking his eyes off the demon and was staying in a position from which he could easily move to defend his friends. Dean felt a surge of gratitude, but it was cut off by the memory of what Cas had done.

What if I never get over that? Dean wondered as he stepped back into that strange control room.

"It's unlikely there's a version of me in this universe, since no one's met any aliens, and let's face it," the Doctor gave them all an apologetic smile, "I sort of cause trouble wherever I go. Not that I mean to! It just happens. Anyway, that means that the woman who called the TARDIS wasn't from this universe, but mine. She's my Amy, and it's absolutely impossible for her to call me. Not even the TARDIS can pick up signals from across the void—it's like sound travelling through space, simply doesn't happen."

"But it did happen," Sam said, his words almost a question.

"Which means there's a link to my universe, also impossible."

"Dear God, does this man think anything is possible?" Crowley grumbled.

"Probably that it's possible to kick your ass right outta here," Dean threatened, gun still trained on the demon.

"You said you were sent to another universe?" the Doctor asked the Winchesters suddenly. They nodded.

"It was freaky."

"I believe you," he said slowly, "Which means it's possible to travel between universes without going through the void. But how?"

Castiel spoke up. "I know nothing of the void, but I do know that the spell used to create a gateway to another reality requires a great deal of energy. From my understanding of it, the power draws the universes together for a brief moment, long enough to send something or someone through."

"So they touch. Fascinating. That's brilliant! Our two universes must be touching in the same way, though the amount of power to sustain it over a period of two weeks must be—"

"An impossible amount," Cas finished. "Nothing could do that."

"Something is," the Doctor chimed, seeming happy. "And we need to find out what, because this is very dangerous."

"People are slipping through, aren't they?" Sam asked, "That's where the missing people are, your universe."

"Most likely, or another universe that's also touching this one. Remember the bubbles-in-a-room image? Picture some of the bubbles drifting together and then touching."

"That's what's happening?" Dean asked.

"No, because universes don't drift like that. The term parallel realities is accurate; they are all running parallel, running on infinitely but never crossing. Ever. The void is the space between."

"So," Dean began slowly, "Universes are like really long, line-like bubbles floating in a vacuum." He chuckled, "What if one pops?"

"Normally, only that universe would end. But at the moment, if, say, I accidentally destroy my universe—"

"He sounds like that's likely to happen. Is it likely to happen?" asked Crowley.

"This universe would also be destroyed, and any others touching it."

"Isn't it hard to destroy an entire universe?" Cas asked seriously.

The Doctor shrugged, evasive. "It's not as hard as one might think. I mean. You know, sometimes things go wrong." He cleared his throat awkwardly. "That's not the point. What matters is fixing this, preventing the universes from touching. First step is finding out just how many are effected by…the…thing causing it."

"You're not a real doctor, are you?" Crowley's voice was dripping with sarcasm.

"Feel free to kick him out at any time, Doctor," Dean commented.

The phone rang again, and the Doctor suddenly looked nervous as he answered it. "Hello? Don't worry, I'm on my way right this second, just have to—no, I'm not off on some adventure, I got lost and—well excuse me if I ended up in Atlanta—what do you mean, picking up boys? I'm not picking up boys—tell River if you want, she's no cause to be jealous, I just ran into—stop talking—fine, fine, I'm leaving right now, see? You can hear the TARDIS starting up. I'll just be a moment."

As he'd been talking, the Doctor began to push buttons and press switches; the consol in the middle of the room began to make a weird, scratchy noise, and the center moved. A second later, Dean almost fell over, and he had to lower his shotgun in order to grab onto a nearby rail. Everyone else in the room seemed similarly occupied with not tumbling off the raised platform.

"What the hell is wrong with this thing?" Dean demanded.

"Nothing at all!" responded the Doctor cheerfully, "She's in perfect order, not having any trouble getting back to our universe."

At last the TARDIS came to a stop, and for a moment no one but the Doctor moved. He seemed fine with this, saying quickly, "Don't go wondering off, I'm just popping in to collect my friends, then I'll take you lot back to your own universe."

Though none of the men, demons, or angels in the TARDIS knew it, when they all simultaneously decided to ignore the Doctor's orders and go investigate this different universe, the Time Lord would not have been at all surprised.

Dean poked his head eagerly out the door but was disappointed to see they'd landed on a boring dark residential street. The houses were small and squashed together, and the air felt like summer. The area looked vaguely British. Or maybe they were in Scotland?

Either way, it was boring, and the doorway to the TARDIS was getting a little crowded with four people trying to see outside without actually leaving the time machine. Dean didn't like Crowley being that close to his unprotected back. He turned around and shoved his way past the demon, who grumbled and said something undoubtedly pithy under his breath.

The consol seemed oddly still and quiet after that brief but jostling trip. Meandering over to it, Dean stretched out a hand to touch a random knob.

"Don't think you should mess with it," Sam advised, striding over and putting his gun down on the bench. "Alien technology. Who knows what those buttons do."

A heavy silence settled over the brothers; Dean heard Cas and Crowley step outside, their voices low and drifting away.

"You look like you're going to a funeral," Sam began after a long moment. "Cas is back. This is good news, remember?" When Dean didn't respond, his brother continued, "He messed up, but it's not like I haven't—and you, too. I mean, we kinda accidentally started the apocalypse. And Cas was always there to help us. He just made some bad decisions."

"Just gonna take time," the other said at last. "I'm glad he's alive. I am."

"Four hours late!" Dean and Sam turned to look out the open TARDIS door; a stunningly beautiful redhead in a bikini was walking towards them, shouting at the Doctor. "Are you ever on time for anything?"

She was carrying bags, and a man was following her. He was also dressed for the beach and carrying a suitcase. The redhead was way out of his league.

"I'm sorry I was late, but I ended up in another universe! Doesn't that count for anything?"

"At least he got here this decade," the man joked. The three had reached the TARDIS, and the two new people paused just inside, taking in the Winchesters.

"So you were picking up boys, Doctor," said the woman, "Not too bad, either." She walked past them, towards a hallway. "Let's put our things away, Rory."

"Nice to meet you," the man—Rory—nodded at them as he passed, and the brothers quickly introduced themselves.

"Now, where're your two friends? I told them not to go wondering off…" The Doctor poked his head outside, calling for the angel and the demon. In a few seconds they were striding back into the TARDIS. "Alright! Just going to pop back over to your universe and drop you all off. I don't even know how to begin addressing the problem of the universes touching, but I'll figure something out. Always do. I'll work on it after the Ponds' vacation." Dean assumed the man was mostly talking to himself, so he didn't comment. "You lot just stay away from Atlanta. I'm sorry, but I don't know where your missing people are, and I could spend a lifetime looking. To recover them I'll have to figure out how many universes are touching, and at what points."

"So we're just supposed to go home and forget it? Maybe put up some caution tape?" By his tone it was clear that Sam wasn't going to take the Doctor's answer. Dean felt the same way—he didn't know how they could help, but they had to do something.

"Well," the Doctor hesitated, "I don't really think they'll want you along for their anniversary trip," he nodded towards the hallway the two newcomers had retreated to.

"You're going on vacation, and people all over who knows how many universes are disappearing into God knows where?" Dean crossed his arms, watching Sam do the same in his periphery.

The alien looked torn, then relented, "Ahhhh you're right, I just can't. I'll have to drop the Ponds off and come back for them."

"Drop us off where, now?" the redhead asked, coming back into the control room, or whatever it was.

"At the beach! You'll be safe, I promise."

"Hah! You've got a lousy track record for safe, Doctor. We're sticking with you."

He smiled. "Then you better change." Glancing around, he asked, "All aboard? Good! Let's go save the multi-verse!"

The TARDIS began to move again as the Doctor leapt about, pulling levers and hitting buttons seemingly at random.

"Do you even know how to drive this bloody thing?" Crowley called, clinging to a rail in a very undignified manner.

"Of course I do! Been driving her for centuries!"

"He's like an old person who doesn't realize how bad he is," Sam joked, and the brothers began to laugh.

The TARDIS shuddered to a stop, and the lights went out.

"What's happened?" Rory and Amy were back, dressed in normal clothing now.

"Dear God, he really doesn't know what he's doing."

"Shut up, Crowley," Cas growled, "This man is very important—"

"Yeah, yeah." The demon waved his hand dismissively.

"No, no, no!" the Doctor exclaimed, "This can't be happening!"

"What is it, Doctor?" the redhead asked. Suddenly she turned a flashlight on. It occurred to Dean that he should learn her name. She was really hot. What had the Doctor said her name was?

"We're in the void," he whispered, leaning his forehead against his palms. "We're stuck in the bloody void!"

"But you said the void was gone!"

"It was! And now it's not. I'm so sorry." He looked up at them. "We're trapped here. Forever."

"That's pretty melodramatic," Sam insisted, "there has to be a way—"

"Without power, the TARDIS can't take us home. She draws her power from my universe, and we're completely cut off."

As if to contradict him, something bright and glowing appeared in the middle of the room. After his eyes adjusted, Dean saw that it was a woman. Her curly black hair was messily put up, and her dress had seen better days. Nice rack, though.

"Hello, Doctor," she said, but her voice was wrong in a way Dean couldn't understand. There was a darkness in it, an emptiness.

"But you're…" He looked like he was talking to a ghost. Maybe he was.

"We are not your TARDIS. We are merely utilizing this form to communicate our final message to you."

"Who are you? No, wait, that doesn't even matter—how are you doing this? Any of it? It's all—"

"Even if you cannot fathom things with your small, finite mine, they still may happen. You believe your little box to be impenetrable?" She laughed, and it made Dean want to sprint from the room screaming. He'd faced monsters since he was a teenager, and this bitch was terrifying him. What was she? "This machine is simple."

"What are you, then?" the Doctor demanded, sounding offended.

"We are the Voidsong."

"And that is?" he crossed his arms. "Go on, we've got the rest of our lives."

She smirked. "You are always the same, Doctor. No matter how many of you we trap here, you always speak with such arrogance, such assurance in your abilities. If you knew us truly, your mind would shatter." She paused. "We told you what we are. We are the song of the void."

"Song?"

"That is the closest word you material things have to describe us. Words, but more than words, a voice, but woven into it layers of meaning that can be interpreted in many ways. We are the Voidsong, we are infinite, and you will waste away here in the blink of an eye while we destroy everything you have ever sought to protect."

The Doctor began to laugh. "You—you're telling me that the void is alive, and you're it?"

"We are not alive."

"Some sort of computer, then?"

"No. You cannot comprehend what we are. We are Voidsong, and you are the very last thing standing in our way."

"Well, bad day for you, then, isn't it? Because I'm the only one you don't want keeping you from your plans, whatever they are."

"We have trapped all other versions of you, Doctor. You are different by only a margin." Her smile was wicked, triumphant. "And that margin will never be enough. Goodbye Doctor. We could kill you, but that will happen in time, and our efforts are needed elsewhere. I wonder, will you also resort to cannibalism? Most of the others did." And with that, she flickered away, and they were left with only the redhead's flashlight to see by.

"Did—did that bitch just James-Bond-villain it up? Really? She's gonna leave us here to die?" Sam shook his head.

Almost everyone else laughed, though Cas only stood awkwardly, looking vaguely confused.

Glancing at the redhead, the elder Winchester commented, "I'm Dean, by the way, and this is my brother Sam." He managed a smile. "And just so you know, no one's eating anyone. We've got bullets to go around if it comes to that."

"I'm Amy," she said hesitantly, "And no one's shooting anyone! We're getting out of here. And who are they, then?" She nodded to Cas and Crowley.

After everyone had been properly introduced, an awkward silence fell. There wasn't a clock in the room, but Dean could practically hear one ticking away the minutes of their lives. Dying in a time machine with an alien. Not how he thought he'd go.

The Doctor, meanwhile, was underneath the glass platform, searching for something. After about five minutes, he cursed, saying, "The Voidsong must have drained all the reserve power! It's useless."

"Great, me and angel boy trapped here for the rest of eternity with your corpses. Just what I always wanted—a bloody wife." Crowley rolled his eyes. "Wish I could starve to death like the rest of you."

"I could kill ya right now if you want," Dean offered amicably.

"Are we resorting to that already?" Rory joked. "It's only been five minutes. We could at least tough it out another half hour." His laugh was awkward.

Cas was making his way to where the Doctor sat, head in hands. Dean watched the angel silently, wondering what it would be like for him to watch his only friends die in front of him, powerless to stop it.

"Doctor," Castiel began; the alien looked up. "This ship is powered by energy from your universe?"

"Yes."

"You have three sources available to you, why not utilize them?"

"You mean us, me and Amy and Rory? There's no way we could supply enough, not to mention I have no way to interface living people with the TARDIS."

"You have the energy, and I can access it. But it will be painful."

"And how will you get it to the TARDIS?"

"That's what we should work out. We have time," Cas almost smiled. He'd made a joke. Dean found himself grinning, then stopped. They were still almost certainly going to die here, unless the Doctor and Cas could somehow magically whip up a solution to an impossible problem.

If he'd asked Amy or Rory, they would have told him that solving impossible problems was almost easy for the Doctor, but he didn't. Instead, he sat quietly, staring at nothing, thinking about the many points of his life that he wished had been different. The things he wished he could take back, all the things he should have said and done. In short, he was preparing to die.

Amy and Rory had somehow found a Scrabble board and were setting up a game. The latter was placing a few candles around the area, lighting them so as to spare the flashlight's batteries. Sam wondered over and politely asked to join; they accepted readily. Crowley also joined, asking less nicely, but hey, there were four places, so why not?

"Don't worry," Amy said as she arranged her letters in front of her, "the Doctor's smarter than he looks. They'll figure it out."

"What's with the bow-tie?" Sam asked in a low voice.

"I have no idea. He thinks it's cool. Whatever you do, don't let him near any sort of stupid hat."

"Oh, God no," Rory agreed. "Remember the fez?"

"Destroy all fezzes on sight," Amy advised seriously.

Dean stopped listening at that point. They had hope, faith, maybe, but he didn't. Not in some random time-traveler and an angel who looked half his normal size without a trench coat. Cas's missing garment was currently residing a million billion miles away, in the trunk of the Impala, nestled next to Dean's oldest and favorite shotgun. He resolved to give it back to his friend if they got out of this.

Time passed meaninglessly; the Scrabble game ended, and someone found a deck of cards and thought Texas Hold 'Em would be fun. Sam invited Dean to join, but he declined.

Without warning, the screaming started. Everyone jumped, and Dean was halfway to where Cas and the Doctor sat beneath the raised platform before he realized what was happening—the angel was tapping into the alien's soul—or whatever he had that was like a soul. Said alien had managed to calm his scream into a whimper, but Dean could tell the man was in horrible pain. Across the room, Sam was physically keeping Amy and Rory from interrupting what the angel was doing. He didn't blame them for wanting to.

"This better work," he mumbled to no one, turning away. What felt like hours later, the Doctor grew quiet, and the lights came back on in the TARDIS.

Despite his obvious agony, the Time Lord sprang up, making his way to the controls, starting the ship up. "We should make it back. Dean, check on Cas," his words were interrupted by the sound of the engines—or whatever they were—making their grinding noise. The TARDIS began to move violently. "See if he's still alive."

"What?" Cas, Dean saw, was lying below the platform, motionless, his arm connected to wiring. The angel's eyes were closed, and the man couldn't tell if he was breathing because of the violent motion of the TARDIS.

Kneeling beside him, Dean checked his pulse; there, but weak. "If you die, you son of a bitch," he threatening in a whisper, "I'll pull your ass back from angel hell and kill you again myself."

The TARDIS landed; Dean distantly heard a sound that was likely the Doctor collapsing, then footsteps that were probably Amy and Rory going to check on him. Suddenly Sam was next to his brother.

"He's alive," Dean said preemptively, "Barely." But as he spoke, Cas gasped, eyes opening.

"It worked?"

"Yeah. Cas, are you—?"

Cas sat up, pulling the wiring from his arm, then nodded. "Good. I can only assume that was what God sent me back for. The Voidsong said that all other versions of the Doctors failed. Perhaps he needed me to escape." He looked up, through the glass. "Is the Doctor alright?"

"I'm fine!" the man in question answered, "Just a bit wibbly. We're back in Atlanta, right where we left."

"Great," Dean said, standing, "I need something from my car. Coming, Sammy?"

"Yeah." Giving one last look at the angel, who nodded that he was alright, the Winchesters left the TARDIS, still cautious in the dark, deserted pre-dawn.

They'd parked the Impala a few blocks down, but the trip didn't take long. Dean remembered the building they'd stopped in front of, and—

The car was gone.

Missing.

He felt that his mouth was slightly open but didn't care. His car—his baby—was stolen. Stolen!

"Man, fuck Atlanta!" he shouted. "I cannot believe this!"

All their guns and supplies—their whole lives—gone.

"Well, shit," Sam shook his head. "Can we not have like, one good day? Ever?"

"The Doctor has a time machine. Maybe we can go back and un-steal it."

The Winchesters turned back towards the TARDIS. They didn't notice the odd thinness of the area around where their car had been, or that roughly ten seconds had passed since they'd left, which wasn't much time for someone to steal a car in.

They also didn't know that somewhere very, very far away, in a London similar to their own in many ways but strikingly different in one, a Detective Inspector was about to receive a very strange phone call, and that the Detective Inspector in question would then call another man, one who specialized in strange things and unsolvable crimes.

The Doctor and his companions will return in

The Case of the Impossible Impala!