A light on the TARDIS console started flashing. It was green, and was nestled amid the many implements on the Communications panel. It was a good minute before the Doctor noticed it. It was another minute before he paid attention to it.

"What's that?" he asked, mostly to himself, but partly to the Ponds, who had just entered the console room.

"It's your control panel, shouldn't you know?" Rory muttered quietly, as the Doctor pulled the screen around, fiddling with the buttons on it. The ship told him they were currently cruising near the year 2010, within the Milky Way galaxy.

"Something's incoming," the Doctor said, somewhat ominously.

"Incoming?" Amy repeated. "Can they even get inside the TARDIS?"

"Well, we're about to find out," the Doctor answered, as something on the console began to ring – an alarm, if anything.

Then all three reeled backwards as the TARDIS was filled with a blinding white light, and a sound that almost pierced their eardrums.

After a few moments, the light began to fade, enough for the Doctor to open his eyes and see the light was contracting to a single point. And in that point a shape was forming. Then the light faded all but completely, and the three were stood looking at a man. He was human in appearance (but travelling with the Doctor meant they could never be sure), wearing a suit and a brown overcoat. Interestingly, the shirt was ripped open, and the man's chest had a strange, glowing symbol on it. It looked as though it had been carved into his skin. The man looked at the three, who were staring at him with a mixture of curiosity and awe. He blinked, taking in his surroundings, or he could have just been blinking out the blood that was trickling into his eyes.

The symbol suddenly faded completely, the skin healing rapidly as it did so. And then the man fell to the floor, crashing down by the stairs to the doors, unconscious.

The room was silent for a moment – even the console's alarm had stopped ringing, as had the warning light and its flashing. The Doctor walked quickly forward, sonic screwdriver at the ready, and swept it over the man.

What it told him puzzled him, and he frowned at the device as Rory stepped past him and took the man's pulse. He then checked his airways and looked the man's injuries over.

"There's nothing wrong that I can see," he reported, as the Doctor swept the man over again. "Aside from these cuts and bruises. Other than that, unless he has internal injuries I think he's just knocked out."

"How did he even get here?" Amy asked. "Doctor?"

"What do you mean there are two?!" the Doctor practically shouted at the screwdriver, before racing up to the console and pressing a few buttons, completely ignoring Amy. The console beeped a few times, and the Doctor pulled something that looked remotely like a hairdryer out from underneath it, before pointing it at the man. The scanner beeped as it took a reading, Amy and Rory watching silently as the Doctor did so. He pressed a few keys on the keyboard, and then pulled the screen around again.

Then he went very, very still.

"Doctor?" Amy asked again.

The Doctor turned, looking at the man laid on the floor, who Rory had turned over.

"This man's body is not his own," he said.

"All right, wanna explain that?" Amy asked.

"It means that there are currently two entities in this body," the Doctor said. "One of them belongs to the body. The other doesn't. Something has taken this body over. And usually when that happens it's not for good reasons. Trust me. I know."

"So... What should we do?" Rory asked.

"Well, we could try and force the entity out, or we wait until he wakes up and talk to it. If it's willing to talk, that is," he added.

"What happens if we try and force it out?"

"Well... I don't actually know what's inside him, so it could do many things. Could be that the thing inside is actually keeping him alive. Could be that whatever's inside won't like being forced out and try and kill us."

"I think waiting sounds like the better option," Rory said.

"Me too," Amy seconded.

They compromised by moving a bed into the console room. That way the Doctor could keep an eye on the man while still tending to his ship, which seemed unperturbed by whoever had penetrated her shielding. Rory checked the man over again, cleaning and patching up his wounds, while looking for any other injuries. He didn't find any.

"He looks like an office worker," Amy said, fishing a tie out of his overcoat pocket, as well as a box cutter with blood on it – probably used to carve the symbol into his chest. Then her eyes widened as she pulled what could only be described as a dagger out of his pocket. It was silver, long and deadly, and it tapered to a point. More like a miniature sword than anything.

"Doctor, what's this?" she asked the Time Lord, holding the blade aloft.

The Doctor frowned for a moment, before coming down the stairs and taking the blade from her. He examined it for a moment, and then scanned it with his screwdriver.

"I've seen one of these before," he mused. "It was in a museum in Earth's distant future."

"Keeping score again?" Amy asked, before the Doctor shot her a look.

He continued as if she hadn't spoken. "It was in a section detailing myths about Earth's past – well, the present to you, but the ancient past to them, when life before a hologram was unthinkable, let alone the Roman and Greek empires. Anyway, one of these was among the items in Earth's religious myths. Apparently, these blades were the weapons of angels."

"Angels?" Amy asked dubiously. "You can't seriously believe in angels, can you?"

"Course I don't," the Doctor replied. "There are far too many variables with religion. It was in the mythology section."

"What was the symbol about?" Rory asked. "It looked weird."

"It looked like Enochian," the Doctor corrected. "Which is a language associated with angels again. What the meaning of that symbol was, I'm not sure," he said. "Enochian is rarely used and it didn't stick around long enough for me to translate it."

"So, whoever this guy is, whatever possesses him is probably really religious," Rory summarised.

The Doctor nodded, glancing at the man lying on the bed. How had he gotten inside the TARDIS? Why had she let him in?

It was a few hours before the man stirred, blinking up at the ceiling high above him. He sat up, the movement slow and careful. His eyes, bright blue, searched the room, before landing on the Doctor and the Ponds. They fixed back on the Doctor, frowning.

"What are you?" he asked in a voice deeper than the one they had been expecting. His accent was American.

"I could ask you the same thing," the Doctor replied. "Seeing as there's apparently two of you inside that body."

The man frowned, looking down at himself, as if he wasn't expecting his body to be there.

"He allowed me to enter," was the eventual reply. "He prayed for it."

"Did he?" the Doctor asked. "Or is that what you simply tell yourself to feel better about the fact there's an innocent human somewhere in the mix?"

The man looked up at the Doctor, his gaze icy. "You still haven't answered my question. You have the form of a human but your heartbeat betrays the fact. You are not like anything I have encountered before."

"I'm the Doctor." The only introduction he would give at the moment.

"And we're Amy and Rory," Amy supplied, seeing as the Doctor wasn't going to. "Humans, though. Un-possessed ones."

The man looked the Doctor over again. "You are impossible," he finally said. "You are a story that was told to me and my brothers. The Doctor, the God without a religion. A face-changer, who was the last of his kind, who stepped in to save humanity when our father could or would not. We were told stories of you to show that not only did we have to bow to humanity, but to those who come from beyond the planet too, as well as accepting that not every man would believe."

"You were told stories of me?" the Doctor asked, proud for a moment, but then his tone became serious again. "This still isn't hiding the fact you've taken over a human body. The Shadow Proclamation probably has laws against this."

The man stood up – slowly, as though the movement took a huge amount of effort. "The Shadow Proclamation would not interfere," he said simply. "This is a matter beyond them."

Amy jumped in then, as she could see the Doctor was about to go all 'threatening Time Lord' on the man, and he didn't look as though he'd have the energy to take it.

"Why do you have to possess a human anyway?" she asked. "You must have some sort of, like, original form."

"My true form would cause your eyes to burn out of your skull," was the answer. "I have learned that it is unwise to test if you are strong enough to perceive it."

There was silence for a moment.

"Burn out of our skulls?" Rory asked, speaking up for the first time. "So why doesn't it burn your-" he trailed off, trying to think of the correct word.

"Vessel. Because it is in his bloodline to accept me as a host – he was more suited than any other. He prayed for it, he was devout, and this was his reward. His name is Jimmy Novak; he has a wife named Amelia and a daughter named Claire. He used to sell 'ad time' for AM Radio."

The man smiled suddenly, as if something amused him. "He has an unhealthy appetite for red meat."

"All right," the Doctor began, "So he's Jimmy. But who are you? The one inside Jimmy. Because whether he prayed for it or not, it's not a picnic for him, you know."

"I know this," was the short reply. "I am Castiel, and I am an angel of the Lord."

None of them had been expecting that. Castiel looked at them all. "You have no faith," he said. "And it is clear to see why. You have all lost too much to believe there is a God. Trust me, I understand this."

It was at this moment that looked down, twisting the tie he'd picked up from the end of the bed through his fingers. He suddenly seemed... sad, almost.

"If you're an angel, where are the wings... and the halo?" Amy asked.

"We are not what humans think us to be. If you read the Bible correctly it describes us as warriors of God. I am a warrior, not a being that sings day and night."

"I would have at least thought there would have been wings," Rory said quietly to Amy. Although, apparently, not quietly enough, as Castiel looked up at them, and somewhere – they had no idea where – thunder cracked and lightning flashed. On the wall behind him, the silhouette of two rather impressive wings formed, foreboding and elegant at the same time. Then it stopped, and they were stood gaping at the man – the angel – in front of them.

The Doctor was the first to break the silence. "Can I just say: those are beautiful wings that you have there. Angel or not, you do have some rather impressive wings. And the thunder and lightning?" he beamed. "Magnificent. How do you do that?"

The question was unanswered, however, as Castiel suddenly fell back onto the bed, wincing in pain. Rory moved forward instantly, ignoring Amy as she shot him a warning look.

"Stay still," he told the angel. "You're clearly weak and this isn't helping. You might be an angel, but you look and react like a human, so I'm going to treat you like one."

"Only Rory," the Doctor said. "The man who can be unfazed by the possibility of an angel."

Rory shrugged, inspecting Castiel, who was looking at him with a mixture of curiosity and annoyance. "If you are an angel," he asked. "Then why are you so..."

"Human," Amy finished. "I always thought angels would be immortal, or at least invulnerable."

"We are," Castiel answered shortly.

"So why aren't you?" the Doctor asked, his annoyance at the possession of Jimmy long overtaken by his curiosity.

"I am... a poor example. I rebelled against heaven and my brothers. As such, I am barred from heaven and my grace is dimmed. I am mostly human."

He winced suddenly as Rory prodded the cut on his head. "Sorry," he mouthed, as the angel fixed his gaze on him.

"What did they do to make you rebel?" the Doctor asked.

"They allowed the 66 seals to be broken. They allowed Lucifer out of his cage. They are trying to make the humans I care about join different sides of the conflict. They do not care that Earth – that humanity – will be destroyed in the process. They simply want to defeat Lucifer and they believe Michael will."

"Lucifer as in the devil, yeah?" Amy asked. "And the Archangel Michael?"

"Yes."

"What are the 66 seals?" the Doctor asked.

"Think of them as locks. There were around 600 in total, but only 66 needed to be broken in order to let Lucifer free. As soon as the first one fell, the others began to break too."

"And what was the first seal?"

Castiel paused for a moment, before quoting: "'The first seal shall be broken when a righteous man sheds blood in Hell.' We laid siege to Hell to try and stop it. But we were too late. So my brothers decided on a new plan: let the seals break and allow Lucifer to walk free. Then Michael could take a Vessel and they could...fight it out. And Lucifer would be defeated, once and for all."

"With no regard for human life," the Doctor finished. "Well, if it means anything, I approve."

The angel looked up. "Thank you," he said. "From someone as such as you, that is a higher praise than I could have hoped for."

"How does a righteous man shed blood in hell?" Rory asked.

The angel sighed. "Hell is... well, there's a reason they give it that name. For one, time is measured differently. You might spend four months in Hell by Earth's reckoning, but in Hell it would be forty years. Imagine, forty years of being tortured, day after day. And at the end of each day, you would be given a choice. Face torture for another day, or torture souls yourself, and never have to experience the pain of being flayed alive, or having every single bone broken one at a time again. A man can only last so long before he is broken."

At his description of Hell, the three looked at each other, expressions mingling between horror and revulsion. Castiel then continued:

"We did all we could to get Dean Winchester out. But those protecting Hell knew what they had. By the time I got to him and raised him, it was too late. He had been broken after thirty years. He had sold his soul to save his brother's life, and gone to Hell for it. They could not hope to find a more righteous man."

"And now you're with this Dean, yes?" the Doctor asked. "Trying to stop the apocalypse."

"That is correct."

"Wait, the apocalypse?" Amy asked. "What year is this apocalypse supposed to happen?"

"2010," Castiel replied.

"Well, it never happened for us," Rory said. "Maybe it means you win."

The Doctor sighed. "I wish I could say that was true. But it's a point of flux – an opportunity. It might still happen and the world you know might change." He shrugged. "Time is always being rewritten."

"So that part was true as well," Castiel mused. "You are a time traveller. Tell me one thing, then, Doctor. Was it also true that you destroyed your own race?"

For a moment the Doctor's smiling air dropped, and everyone saw the deep sadness in his eyes. The regret. The shame. He nodded. "Yes, it's true," he said quietly. "It was the only way to stop the war."

"Then perhaps you understand this better than most. I gave up everything for Sam and Dean Winchester. I have killed my own brothers, angels I was raised with. Just, tell me: Is it worth it?"

Suddenly, Castiel looked very small. His confidence, his self-assuredness, gone. He just looked... human, lost, looking for answers. Looking to the man he'd been told stories about, back when his family had been whole. He fiddled with the tie in his hands again, looking down.

"Only you can know that," the Doctor said. "For me, sometimes it is, sometimes it isn't. You just have to keep going. And see the beauty that's still in the universe. And not every day is a bad one. You just have to remember why you did it, and why the world will be better for what you did. Try not to dwell on the bad points. If you do that, it'll destroy you. Oh, and don't ever try and do something alone. That will definitely destroy you. And make sure they're good people. Why do you think I bring these two along?" he asked, smiling again as he gestured to the Ponds.

The angel nodded. "Can I borrow a phone?" he asked. "I lost mine during the banishment."

"Of course!" the Doctor practically shouted. "It was a banishing sigil." He grinned, previous sadness immediately forgotten. "So those actually work? Do they have to be carved into your skin, though?"

"No, but they have to be drawn in blood, and there wasn't enough time to draw one on the wall. Do you have a phone in this machine of yours?"

"I do," Amy said, pulling hers out. "Who are you going to phone then?"

"Dean. We are in a precarious position at the moment."

"And what are you going to tell him?" the Doctor asked. "That you woke up in a time machine, and you've been talking to an alien and his two human companions?"

"Are you suggesting I lie?" Castiel seemed mildly shocked at this.

"Well, imagine if you got a phone call saying you've met someone with a time machine. Now, I can't imagine that the people you're with won't want to use it for some reason. And there's the possibility that your angel brethren might find out, and honestly, I've been trying to keep a low profile. I don't really want a heavenly host after me."

Castiel nodded. "Understandable." He sighed. "Fine," and then he dialled a number.

They could only fully hear Castiel's end of the conversation, but whoever this Dean was, he seemed to be genuinely concerned for the angel's health. They caught a few fragments of the other end.

"Dean."

"-the hell are you?"

"A hospital."

"-you OK?"

"No."

"-wanna elaborate?"

"I just woke up here. The doctors were fairly surprised; they thought I was brain dead."

"-hospital?"

"Apparently, after Van Nuyes, I suddenly appeared bloody and unconscious on a shrimping boat off Delacroix. I'm told it upset the sailors."

"-just in time... pop Satan's box-"

"How?"

"-it's a long story... zap over here-"

"I can't zap anywhere."

"What do you mean?"

"I'm saying that my batteries are drained."

"-angel mojo?"

"I'm saying I'm thirsty, my head aches... I have a bug bite that itches no matter how much I scratch it. I'm just saying that I'm incredibly..."

"Human."

Castiel sighed in answer, looking to the heavens – well, the ceiling of the TARDIS.

"Wow."

"Look, my point is, I can't go anywhere without money for...an airplane ride," he cast a quick look at the Doctor at this, clearly uncomfortable with lying. "And food. Or pain medication ideally."

"-wire you the cash."

"Dean, wait. You said no to Michael. I owe you an apology."

"Cas-"

"You are not the burnt and broken shell of a man I believed you to be."

"-I appreciate that."

"You're welcome."

He hung up after that, passing the phone back to Amy. "Thank you."

"What did you mean by saying no to Michael?" the Doctor asked. Castiel sighed in response again. "Dean Winchester is a Vessel of Heaven. He is the Sword of Michael. His Vessel. But every angel needs permission to enter their Vessel. I needed Jimmy's. Lucifer needs Sam Winchester's. But both of them are saying no. Which is why both heaven and hell are seeking them. They are the Vessels that will decide the conflict. But now it appears they have found a way to put Lucifer back into the pit."

"How?"

"It involves the Horsemen."

"Horsemen as in Horsemen of the Apocalypse?" Rory asked.

"Yes. War and Famine have already been... dispatched. Now they are going for Pestilence."

"How do you dispatch a Horseman of the Apocalypse? "

"Their power is derived through a ring on their finger. Cut off the ring, you cut off the power...and usually the Horseman doesn't survive. I assume this new plan involves the rings."

"And once you have Pestilence?" Amy asked.

"Then we find Death."

The Doctor whistled. "Blimey. And I thought our lives were difficult sometimes."

"Be that as it may, I need to get to them. I doubt Pestilence will go without a fight."

"Are you sure? You've barely recovered from... whatever it was before that brought you here. Why did you need to banish yourself anyway?" Rory asked.

"Zachariah – another angel – had taken Sam and Dean's brother hostage. They needed to get into the Green Room, and there were four angels guarding it. As I said before, there wasn't enough time to draw one on the wall, and we needed to move quickly. Adam's blood had enough in it to allow Michael to use him as a Vessel without destroying him. I fear that they did not get him out in time."

He paused for a moment, frowning. "Although it seems they may have... put Zachariah down. I cannot feel him anymore."

"Put him... down?" the Doctor asked.

"Yes," Castiel sighed. "Another of my brothers lost. But then again, Zachariah was a dick."

Amy grinned at the use of the word – it was an unexpected contrast to the rigid formality of Castiel. "Well, at least rebelling gave you a sense of humour," she said.

While he had been explaining this, Rory had gone to the first-aid kit that he'd been using to clean the angel up. He returned with a small pill packet, some water and some cream.

"For the headache and the bite," he said. "I assume you know what to do with it."

Castiel looked a little shocked, but he took the water and pills. "Thank you," he said, emptying them into his mouth and swallowing.

"Yeah, well, everyone seems to forget that I was a nurse before I joined these two," was the reply.

"We don't forget," the Doctor protested. "OK, so maybe we do, sometimes, but frankly, you're defined by more than your profession, Rory."

"Yeah, Last Centurion, remember?" Amy added, nudging Rory with her elbow.

"You do choose your companions well," Castiel told the Doctor, gingerly standing up and mounting the stairs to the console. "Your ship is..." he paused, frowning. "It is sentient. I can feel its soul."

"Really?" the Doctor asked. "Maybe that's why she let you in. Saw you were in a bit of bother and thought she'd help."

The angel nodded absently, placing a hand on the console. A brief smile lit his features. "She is singing. She is happy... because you are happy."

He removed his hand, turning to the Doctor. "I am glad to have met you. Although we may not agree on certain matters like my use of a Vessel, or your beliefs of angels, your friends and your ship show me that you are a good person. Perhaps better than in the stories we were told."

"Thank you," the Doctor said quietly, smiling. "Now!" He clapped his hands, suddenly business-like. "Let's see about getting you to these Winchester boys, shall we? It'll save you getting a plane."

He grinned at the expression on Castiel's face. "It'll be just like taking a bus."

He moved to the keyboard on the console, tapping a series of keys, and pulling a lever. The TARDIS rocked and hummed in response, Amy, Rory and the Doctor having to grab the nearest object and hold on. Castiel simply stood, looking with an expression between amusement and confusion, his balance perfectly centred.

"She appears to complain, however, that you leave the brakes on," he said above the noise.

"Well, she's going to have to deal with it!" the Doctor complained. "Honestly, who's the one flying this thing?!"

In response, the TARDIS bucked, sending the Doctor flying into the railing. "All right," he grumbled to the air. "I know it's you really."

Amy and Rory laughed. "Having an argument with the Mrs are we?" she called.

"Oh, shut up!" the Doctor shouted back, as the noise and rocking settled. "Right then," he said, pulling the screen round to face him. He fiddled with a few levers, and read the data. "We are at the... Serenity Valley Convalescent Home, Davenport, Iowa, May 2010. And it appears your friends are already here." He pointed to the screen, and Castiel peered at it. It was security footage from the home, showing Sam and Dean, lying on the floor, looking very... ill. A man stood over them speaking. A green ring glinted on his finger.

"Pestilence, I assume?" the Doctor asked, Castiel nodding in reply. "I need to go," he said. "I thank you for the help. And the pain medication."

The Doctor nodded as Amy handed Castiel his blade back. She pulled the tie from his hands and in a few swift movements, tied it around his neck. "There," she said approvingly. "Dressed for battle."

"Try not to exert yourself too much," Rory added." You don't want to end up in another hospital. After this, make sure you drink water and get rest. Your body's probably exhausted."

Castiel nodded, placing the blade in his pocket. Then he moved swiftly to the door and left.

Watching on the console screen, the trio saw Castiel burst into the room where the two brothers were lying on the floor.

'How did you get here?' Pestilence asked, shocked at his sudden appearance.

"I took a bus," was Castiel's reply, with a glance to the security camera.