Just to be sure, the hunters had tied Amy's scarf over her eyes for the last hour of the drive. Sam had tried to explain that it wasn't because they didn't trust her; it was simply a safety precaution to keep the place truly off the map. Dean however insisted that their lack of trust in her was precisely why they didn't want her to know exactly where their bunker was. She played along to give their minds some peace, but Amy would have had just as little clue as to where they were without the blindfold. Unicorns had a tendency to wander from place to place, but keeping track of where those places were wasn't exactly part of it. Nomads, with not a care in the world of where they were going.

"Home sweet home." Dean smiled as they walked into the reading room of the large building, pulling off his jacket to sloppily hang it over a chair. Sam carefully removed the scarf so that Amy could see, and while she tied it back around her neck, she looked around with fascination. Her old cabin and this magnificent piece of architecture were worlds apart. These books had frames that didn't crumble at the touch, furniture which shone with their polished wooden surfaces; not at all like her withering books and things covered with lint and dust. There was a cheerful smile on her lips as she began examining the rows upon rows of books. Titles she had never seen before, monsters she had never heard about, this place was offering her all the knowledge she could ever want. It was highly unlikely that she would put it to good use, but the knowledge itself was what was enticing her, not the thought of hunting. She had killed one vampire, and that was good enough for her.

"So why did you pop into the car anyway, Cas?" Sam looked over at Castiel, who was concentrating his visual focus on the preoccupied unicorn.

"I did it to observe." Sam raised his eyebrows, glancing off at Amy before looking back at the messy haired angel.

"Observe.. Amy?" Sucking in a breath Castiel looked over at Sam as though he was explaining something really basic to a toddler.

"Yes, I came to observe the first specimen of unicorn found since before the dark ages. Why is that so difficult to comprehend?" Dean returned to the room, armed with a six pack of beer and a smile, putting it down onto the table as he looked at Castiel.

"I take it they're rare?"

"They're more than rare. Alpha monsters, are rare. Albino lions, are rare. Unicorns, are not supposed to even exist down on earth." Sam pulled out a chair to sit down, grabbing the beer his brother was handing him to twist off the cap, taking a sip.

"So why are they down here?" Castiel moved out his hands before dropping them to thump them against his trench coat in a defeated gesture.

"I believe I mentioned it before that Gabriel was supposed to herd them back to heaven, but he failed in bringing them all back." The two brothers nodded.

"But those that were left, shouldn't they have just, reproduced and gone up in numbers? Why are they so rare?" Dean took a swig of his beer. It seemed that they had stumbled upon something quite complicated, and before they made any kind of move, he wanted to know what exactly they were dealing with. As far as he knew, Castiel was the only reliable source of unicorn lore.

"Unicorns are not normal animals, Dean. They are holy beings and will not breed on a whim." The angel spoke as though he was offended by the mere thought, his eyes narrowed on the brash hunter, who simply held up his hand with a frown. "Geez, sorry."

"No doubt, when they scattered as Gabriel failed to herd them, most of them ended up alone." He glanced over at Amy, frowning slightly as she had taken a seat on top of the low bookcases, leaned against the massive white pillar, a book in hand. The decorative, yet deadly weapon on display had been forced to give up its precious spot, now taking up residence on the floor.

"I believe that they had trouble both adapting to life after the serpent on earth, as well as finding each other. Many undoubtedly went mad with the amount of poison in the world, as tainted as it is. As such, their numbers dwindled." Dean frowned and leaned back in his seat, throwing up his legs onto the table.

"So how long can a unicorn live?"

"If untouched by evil? Forever." Castiel's reply came quickly, though both Sam and Dean had a bit of trouble understanding exactly what the angel meant. "And what exactly counts as being... Touched by evil?" Castiel heaved a sigh. It was no wonder that they had no accurate information, what with all the ridiculous stories human kind had made up about these creatures, but it was like talking to monkeys.

"It means, that they can only be slain by great evil. For an example, Crowley would have no trouble killing her. However, if she was to be slashed or shot by a desperate human, she would walk away. Injured, but she would not die. I also believe they are able to end their own lives." Dean raised his eyebrows, glancing off at Amy with his hand moving towards his belt. "You will not test this theory!" Castiel glared at Dean with narrow eyes.

"Not even I have actually seen a unicorn get injured, thus I can not with certainty say that she will not die if you shoot her. I do not believe she would, but this is far too precious a specimen to test such things on." Dean shrugged with a grin, taking a mouthful of beer. This was all highly informative, but also amusing. Sam rolled his eyes at his brother before turning his attention fully to Castiel, leaning over the table with his hands locket together.

"Cas, didn't you say they were herded back to heaven, most of them? Why does it matter if they are rare on earth?" Castiel tipped his head slightly to the side to frown at Sam, who held up a hand. "Sorry. More, than rare." That seemed to appease the angel who straightened out, relaxing.

"The unicorns in heaven are of no use to us. Heaven is on lockdown, and for all we know, we might not ever be able to open it. That would mean the extinction of one of our Father's most beloved creatures. I can not let that happen."

"Well they wouldn't be extinct, they would still be there, right?" Dean frowned, looking over at Castiel. "A heaven untended to by angels will crumble. We are not there simply for show, Dean, we are part of the balance of heaven. If we are not able to open up heaven, it will fall. It will take time, but it will fall."

There was a pause where the words were simply allowed to sink in, before the silence was broken yet again by the raspy voice of the angel.

"Unicorns that have adapted to earth would be able to aid us greatly."

"And how would they be able to aid us, exactly?" Castiel frowned in confusion as he looked over at Dean. Had he not been listening to his information?

"Last time I checked you liked having things with you that could kill monsters and demons. You almost died several times for the demon blade and the colt. Well, there you have a colt!" Castiel motioned towards Amy with a hint of aggression, wishing for Dean to understand the usefulness of the creature they had come across. Amy raised her head and looked back at them with a frown.

"I am technically a filly, and I'm not quite that young."

...

After a couple of hours, Sam had managed to pry Castiel away from his job of observing the unicorn. Retreating to the storage room for privacy, he heaved a sigh before looking at the angel.

"You took me away from observing her to look uncomfortable?" Sam's lips twitched with a smile as he let out a chuckle, shaking his head.

"No, no, I just.. Do you really think she can help us? Because let's be honest, we could use some help."

"I am always honest. Well, I didn't use to be, because I was conceited and mad with power, but now, I am always honest." Sam waved a hand at Castiel. "Yeah yeah I get it. But I mean, should we.. Train her, or something?"

"It would be wise, yes. That way she could efficiently protect herself when they come for her." Sam blinked as he stared at the angel. "When they come for her?" Castiel huffed out a light chuckle with a slight smile.

"We are not the only ones who could have use of a unicorn. If the angels, or demons for that matter, find out that there is an earthly unicorn, they will wish to use it."

"Huh. Is she really that powerful?" Castiel tipped his head to the side with a slight scowl, rolling a shoulder. "It depends on the definition of powerful. Her particular abilities, both as a healer and as a weapon, are immensely useful in the current situation."

"You mean, the war?"

"Yes, the war. Hundreds of angels are being slain; imagine having a creature on your side which has the ability to resurrect them."