Disclaimer: I don't own 'Supernatural' or 'Merlin'; they belong to their respective creators, and I'm just borrowing them for this story

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The Cup of Life

"Damnit, Cas!" Dean said, looking over indignantly at the angel as they reappeared on a mountainside, a cave just visible a short distance up the hill from their current position and the sun setting in the distance. "You couldn't have just told us where to go?"

"The time when the ritual may be performed is this night, and we did not have the time to travel here by more conventional means if we were going to stop it; I concluded that this was a scenario where it is easier to take action than wait and explain," Castiel explained.

"Sending us in to a nest of demons without any chance to prepare is easier than giving us time?" Dean asked, glaring in frustration at his friend; he would have expected this stunt from the Cas who'd dragged him out of Hell, not the Cas who'd helped them take out Famine and the Whore…

"You are both already armed from our time in Camelot and they will not be expecting an attack at this time; they have no reason to believe that I would be this aware of the Cup's current circumstances, and they are more intellectual than powerful compared to the demons you are used to facing," Castiel explained. "It has only been a few hours since we originally went to Camelot, and the demons only completed their work on corrupting the Cup a short while before I came to you; the rituals to corrupt it were in progress before I was aware that it was in peril, but there is still time for us prevent them completing the rituals that will allow them to channel the Cup's power to the extent required for the plans I described."

"So… we act now and deal with them while they're weak or we're up against a bunch of Azazel-level bad guys that we maybe can't kill with the anti-demon weapons?" Sam asked, allowing Castiel to nod in confirmation before he looked over at Dean with a resigned sigh and pulled out the dragon-forged angel blade that Castiel had given them. "Well, we'd better get on with this…"

"Yeah," Dean said, drawing his own dragon-blade with one hand while checking his gun before leaving it in his other hand. "Like you said, sooner the better, eh?"

"Just one thing, Cas," Sam said, looking curiously at the angel. "How did you know about what they were up to with the Cup so quickly?"

"I have been tracking the lost heavenly weapons with some assistance from Balthazar; he took some of the armoury, but the Cup was one of many items that were mislaid long ago," Castiel explained, before he actually shrugged in a slightly awkward manner that put Sam in mind of the angel's reaction to Chuck's work. "It is a… personal interest of mine."

"You're a fan of the legends it's acquired?" Sam said, looking at the angel in surprise.

"It represents your drive to go beyond what you know and seek the aid of higher powers without placing yourself above them or making yourself dependent on them," Castiel said, before his eyes narrowed as he glanced up at the cave he had previously indicated. "They are coming; use the blades I have given you to kill them, and you will prevail."

With those words, the angel vanished, leaving the Winchesters to draw their guns to accompany their blades- it might be a superficial gesture, but it made them feel better-, and charge towards the indicated cave.

Neither of them might like how quickly they'd been dropped into this, but the quicker they had it dealt with, the sooner they could get back to more regular hunts that didn't involve such large-scale consequences.

Most of the time, Dean hated Enochian wards; not only did they deprive him and Sam of one of their best allies- the other angels he'd met might be mostly dicks, but right now he'd probably be willing to deal with Zachariah again if it meant having back-up-, but they couldn't even see the damn things to scrawl over them and render them useless.

On the brighter side, however, as two men emerged from the cave with the black eyes that clearly indicated a demonic presence, they did have another advantage he hadn't considered; since the demons had been warding against angels in such a remote area, they'd probably never considered even the possibility that they'd be attacked by anybody, even if humans probably didn't really 'rank' as a threat to people scared of angels. As a result, the demons attacking them did such an amateurish job of their assault that it was relatively easy for Dean and Sam to shoot them both in the heads as they charged towards the brothers, the force of the shots sending the demons to the ground long enough for the Winchesters to stab them with the blades that Castiel had given them.

After pausing a moment to ensure that there was no sign that anyone else had noticed them, Dean and Sam advanced further into the cave, but it didn't take them long to discover the end, which had been carved out into a significantly larger room than the corridor leading up to it suggested. At least half the size of the main hall in Camelot, the end of the cave had various carvings on the walls and an ornate table stood in the middle of the room. The Cup of Life held pride of place in the centre of the table, slightly tarnished but otherwise apparently unaged since they had seen it in Camelot over a thousand years ago/a couple of hours ago (Time travel; the damn thing was apparently complicated mathematically and obviously murder on the tenses), surrounded by around six demons dressed in long dark robes; the shadows might conceal more, but it couldn't be more than four others if they were.

It was a small group considering what they were trying to do, but given how chatty demons tended to be- Ruby and Lilith had kept their plan between them for a reason, after all- Dean assumed that they were keeping this whole thing quiet to ensure that nobody blabbed before they were ready; he and Sam probably wouldn't even know what they knew if Cas hadn't been looking for the Cup.

"Hi there," Dean said, grinning as the demons turned to look at the new arrivals in shock, the brothers aiming their guns at the demons with one hand while holding their blades in the other. "Sorry to but in, but we're going to need that Cup."

"You cannot stop us-!" one of the demons began to yell, only to halt his sentence as he yanked another demon into his path when Dean hurled the blade towards his foe, the other demon taking the blade in his back and collapsing with the familiar spark and smoke that represented a demon dying in its meatsuit.

Cursing his bad luck- it had been a risky move, but he'd really hoped the element of surprise would be enough-, Dean allowed Sam to take point with his own blade while he pulled out Ruby's old knife, grateful that he'd been the one carrying it rather than Sam, Sam taking out two demons as they charged him before Dean was armed with a useful weapon once again. At the sound of chanting, Dean glanced back at the Cup and saw that the demon he'd nearly stabbed was chanting something over it- his brief theory about that guy being the leader was looking increasingly more likely-, but he didn't have time to think about it before his attention had to return to the demons attacking them.

With numbers working against them, Dean quickly traded his gun for a flask of holy water in one of his inside pockets and began to toss it around, smiling as the demons retreated with agonised hisses; these guys might have been smart enough to find the Holy Grail, but they clearly lacked a lot in terms of demonic power. With the demons distracted by the pain of the burns, Dean switched his focus back to the blade and began to slash out with it, slicing through the throats of a couple of attacking demons before they could get away. Risking a glance, he was pleased to see that Sam had picked up his previously-thrown blade and was using it in conjunction with his own weapon, stabbing two demons in the heart with relative ease. With those demons down, Dean quickly turned to face the table where the Cup was located, his eyes quickly falling on the last demon standing.

"You can't stop us!" the apparent lead demon said once again, grinning maliciously at them as he stood beside the Cup, his hands raised above it with a blade in one held over the palm of the other, clearly preparing to release his blood into the Cup. "The Ritual is almost complete-!"

"Too bad 'almost' doesn't count, asshole!" Dean yelled, pulling out his gun once more and firing it at the demon once again. The demon didn't seem to react to the first bullet as it struck him in the chest, but subsequent shots forced him further and further back from the Cup, inch by inch, until he had backed his way almost completely up to where Sam had sneaked up behind their enemy. Still dazed by the bullets despite their relative uselessness against him, the demon was unprepared for Sam stabbing him in the back with the blade, the meatsuit collapsing to the ground as Sam yanked the knife out.

"Huh," Sam said, looking down at the body before he glanced back at Dean. "That was… actually rather simple."

"No wonder they wanted the Grail; probably figured they'd never get any respect if they didn't get a boost," Dean said, shrugging dismissively at the fallen enemy before he looked back at Sam as he picked up his dragon-forged blade and indicated the central table. "Shall we?"

Nodding in agreement, Sam walked over to the table with Dean close behind him, the two Winchesters taking up position on either side of it. Raising his blade, Dean exchanged a brief glance with his brother before they both brought their weapons down on the Cup. The blades cut through the Cup like it was made of butter, severing the top part of it away from the stem without any real sense of resistance. The blades themselves seemed to dissolve as soon as they'd parted company with the Cup- Dean wondered if that was a design flaw or just the consequence of destroying something like this-, but the Cup remained separate as Sam and Dean looked at it, the stem standing on the table while the top lay alongside it, showing no sign that it was going to come back together.

"Whoa…" Sam said, looking over at Dean after a moment's silence. "We just destroyed the Holy Grail…"

"Yeah…" Dean said, looking solemnly at the Cup's shattered remnants before he looked over at Sam with a smile. "Well, we just wrecked an ancient relic, but on the bright side, we did get knighted by King Arthur."

"He wasn't a king yet, Dean; Uther was still alive, remember?" Sam pointed.

"The guy was catatonic and virtually useless; Artie was king and that's that," Dean said, looking firmly at his brother.

"Our lives are really weird," Sam said, looking reflectively out of the cave.

Regardless of his casual manner, Dean couldn't quite believe what they'd just gone through himself; travelled back in time to a location that was meant to be myth, worked with the most legendary warriors of all time, met the most powerful wizard to ever exist, and discovered and destroyed a relic that was meant to have belonged to Jesus Christ himself (Even if Cas had admitted that Jesus was a bit more complicated than what they knew)…

"And now they're gone," Sam said suddenly.

"Huh?" Dean said, looking at Sam in confusion.

"The knights," Sam clarified, glancing down at his attire. "We just fought alongside them a few days ago… and they've been dead for centuries."

"Yeah, but people remember them," Dean said, looking at Sam with an encouraging smile. "How many people can you say that about a millennium after they're dead?"

"I know, it's just… it's weird, you know?" Sam said, sighing as he looked down at the remains of the Cup of Life. "All that effort to break a cup…"

Dean was aware that they'd need to call for Castiel to get them back to Bobby's soon- among other things, he was looking forward to using a toilet that didn't smell like animals had been in it as well-, but he'd worry about that later; right now, like Sam, he wanted to spend a few moments reflecting on the people they'd just met.

Sometimes, being a hunter gave you nothing but crap, trolling through the underbelly of the world to deal with the kind of monsters the rest of the world had nightmares about as kids, but sometimes, every so often, you got the opportunity to see something that was actually kind of cool.

The moment when he'd learned that angels were real might have been questionable in the aftermath, but Dean knew for a fact that nothing was going to take away his sense of wonder at having had the opportunity to become a knight of Camelot…

As he sat in the part of Heaven that had become his private sanctuary since his return, Castiel pondered his recent mission.

He had disliked having to deceive Sam and Dean about his intentions during this mission, but the deception was necessary; explaining how he intended to use the power of the Cup in his war against Raphael would have taken too long, and it was easier to simply seek their aid in destroying it and take everything else from there.

It wasn't like he had been lying about the dangers that the Cup could pose after the rituals that the demons had performed on it and his inability to trust any of the other angels with its safety; he'd just exaggerated the scale of the damage that the ritual had done. Theoretically, he could have performed a counter-ritual to turn it back to its original purpose, but he lacked the time to purify the Cup on his own, and there were too many other things going on for him to find other angels that he could trust to help him do it.

Even the ritual that he'd provided for them hadn't done exactly what he had said it would do. While the ritual that Merlin had begun in the past with his aid had allowed him to weaken the Cup of Life to the point where it could be destroyed, the blades that he had provided for Sam and Dean had actually been linked to him through the connection forged through his power being channelled into them while Kilgharrah breathed on them, with the result that, when the Cup's physical form had been destroyed, its power had passed into him, rather than simply dispersing so that it could be eventually restored like it had when Merlin had killed Nimueh.

He hadn't liked having to do something like that to one of Heaven's most precious relics, but it was necessary to ensure his continued ability to operate as an angel. With things in heaven becoming ever more unstable, he would need additional reserves of power to call upon if he should be cut off from Heaven like he had been last year, particularly if Raphael gained further power, and if that meant taking the power of an ancient relic to sustain himself…

It wouldn't be completely smooth, but this way he'd be able to maintain his 'access' to Heaven's resources without actually needing to be a full part of the heavenly host; even if they tried to kick him out again, he'd have access to the power reserves needed to retain his full range of abilities.

The loss of the Cup of Life was a shame, but it would all be worth it once Heaven was stable and Raphael could no longer attempt to start the Apocalypse all over again.

Sam and Dean would understand when everything was over…

AN: And there we have it; Sam and Dean's time in Camelot has concluded, the Cup has been destroyed, and I've achieved my goal of writing a crossover that's in canon with both shows; hope you liked it.

To those who might want a sequel, I have an idea in mind, but I'm saving it for later; I've got other things I'd like to get through first…