A/N: This is set directly after 10x3, so spoilers up to there. You've been warned. Oh, and I'm sorry… I'm so, so sorry. In my defense, this started as a happy, fluffy little thing… (If you're in the market for happy Winchesters, you can read my previous Supernatural fic. It's called Cavities.)

Disclaimer: I don't own Supernatural or any of its characters.

Castiel learned that hard way that research was incredibly, unbelievingly, one-hundred percent boring.

Though the newly restored angel tried desperately to focus on the book in his lap, he just couldn't seem to make the inked words and ancient drawings make any sense. Perhaps Castiel would have had more success if he wasn't so busy sneaking worried peeks at Dean out of the corner of his eye.

After the first relaxed night of re-humanization, Dean had gotten edgy again and was prepared to pick a fight just about anywhere. It wasn't nearly as bad as it had been in the days leading up to the fight with Metatron, but it was certainly noticeable. At least, Castiel saw it. Sam was blinded to the truth by the fact that his brother was back.

The silence in the library was strained, to say the least, a product of the harsh words that had been exchanged just moments prior between the two Winchesters.

Eventually, Dean spoke, his voice cutting the tension like a butterknife would butter. "So what's been going on in monster-land?" he asked, pushing his own book away. "What's Crowley been up to lately?"

Sam gave him a dubious look. "Wouldn't you know?" he responded. "After all, you were his 'BFF.' "

Dean leveled a harsh gaze at his brother. "Those were his words, not mine." Some part of him was expecting Castiel to interrupt by asking what a "BFF" was, but was mildly disappointed when he didn't.

Sam raised his fingers from his laptop's keyboard ever so slightly, a sign of submission. "I didn't mean it that way," he said defensively.

Dean let it go. "What about someone else?" he pushed. "Someone like Abbadon? A monster that needs its throat cut out?"

Sam sighed and ran a hand through his hair. "Shouldn't we be asking you those questions?"

Castiel broke in in an attempt to reroute the conversation. "Has the Mark been troubling you, Dean?" If he had been able to, Castiel would have kicked himself. He had gotten so good with his "brain-to-mouth-filter" lately. Now would be the one time the filter failed to filter.

Dean turned to look at him, his expression exasperated. "Did I miss something? Is it 'Interrogate Dean Day?' " he asked and his tone perfectly matched his expression, "I haven't had any urges to start stabbing people, I'm not puking my guts out because I haven't killed anyone – Yes, Mom, I'm fine."

Castiel pressed his lips firmly together. "I wasn't implying you weren't," he assured the hunter, "I was just… I believe the phrase is 'passing the bean dip.' "

At that, the brothers burst out laughing, albeit unwillingly.

Castiel looked quickly between the two of them, confused by their reactions, then centered his eyes on Dean. "What did I say?"

Dean composed himself, though his mouth was still turned upward. "Cas, man," he said, "Usually you don't tell people when you're changing the topic. It's something you do subtly."

Castiel nodded in understanding. "I see."

Sam shook his head, still grinning, and went back to sifting through search results on his laptop.

Dean moved to return to his own research, but his gaze lingered a little longer on the angel's face. "Passing the bean dip…" he muttered, thoroughly amused, then he pulled the book he'd been looking through back in front of himself.

Despite the "bean dip" having successfully been "passed," Sam wasn't quite ready to let the previous topic go. Even if it had been the demon in him talking, the things that Dean had said to him during the treatments still bothered him. "Not that I'm trying to start anything," he began, "But did you hear anything about some end-of-the-world type plans during your… adventure?"

The stony expression was back. "If I had," Dean replied, the words short and clipped, "Don't you think I'd have told you already?"

Sam shifted uncomfortably in his seat. "Of course," he said.

Dean's shoulders tensed and he glared at Sam. "But?" he prompted him, picking up on the hesitation in his voice.

"Nothing," Sam said placatingly, but the memories from the previous night wouldn't leave him alone and Sam couldn't resist adding under his breath, "Assuming that you'd actually tell us."

At that statement, it was obvious even to the socially-inept Castiel that Dean was trying very, very hard not to slug his little brother.

"And what is that supposed to mean?" Dean demanded through clenched teeth. "Didn't we already go through this? I passed all the tests – hell, you tossed a gallon of freaking holy water in my face!"

Sam set his jaw, determined not to fuel the fire. He'd pushed Dean far enough. So, rather than continue down his current trajectory, he simply stood up, quietly closed his laptop, and left the room.

Dean watched the door for a moment after he disappeared, wondering if Sam would come back, but when he didn't, Dean relaxed a bit into his chair. He glued his eyes to the book in front of him, intent upon not to letting the altercation get to him.

Castiel sat soundlessly in his armchair, observing the still rather red-in-the-face hunter. He couldn't help but notice that Dean hadn't actually provided a direct answer to any of Sam's inquiries.

The angel opened his mouth to say something – anything – but immediately closed it again indecisively.

Dean was grumbling to himself and most of the words were inaudible, but as he got louder, there was one phrase that, had Castiel been capable of heart attacks, would have given him one.

"Sometimes, I swear I could kill that boy."

Castiel's eyes went wide and he felt his grace well inside him. This wasn't the Dean he knew. His Dean would never say that.

Dean's thankfully very green eyes flicked up to the angel, who was still staring. "What? Do I have something in my teeth?" he asked rhetorically, some of the anger having left his face.

Castiel squinted at him, analyzing every millimeter of those green eyes. "I think I was mistaken," he said, still searching for any hint of black. "It's nothing," he added, finally convinced that there wasn't any.

Dean watched Castiel watch him for another moment, before shaking his head.

Castiel breathed a small sigh of relief when Dean's posture relaxed. He had overreacted. But better safe than sorry – wasn't that what the saying?

Yet after another minute or two passed, Dean's presence was radiating anger once more.

"Dean…" Castiel said slowly, worriedly, "Are you feeling alright?"

Dean fixed his fuming gaze back on the angel. "I'm fine," he spat.

Castiel nodded, unconvinced.

Dean gave an irritated huff and slammed his book shut. "I said, I'm fine." With that, he threw his chair away from the table and rose up to his full height. "I don't need you to play Mommy to me," he went on, "I'm a big boy, thank you very much."

Castiel was truly uneasy now. This was taking things a bit far – even for Dean.

I could kill that boy.

All it took was for Dean to take a single step toward the door for the angel to put two and two together.

With a growl of "No!" Castiel leapt at the hunter, knocking him to the floor.

Dean twisted in his grasp until he could peer over his shoulder at the angel. "What the hell, Cas?"

But Castiel didn't reply, rather he just stared sadly down at his friend, knowing what was to come, then shouted for Sam.

It was when Dean began to struggle in his grasp that Castiel finally let his eyes glow blue. "Stop."

Though the word was uttered softly and gently, it had an immediate effect on the agitated man. As if he were being forced to take orders.

Sam came crashing into the room, demon knife in hand. "Cas?" he asked, taking in the scene, "What's going – oh."

Dean shuffled again, this time turning toward Sam. "Would you tell him to get off of me?"

Sam swallowed and shook his head slowly. "I'm sure Cas has his reasons," he replied.

Castiel tightened his grip on the hunter and said by way of explanation, "I don't think the treatment had a lasting effect."

The words brought Dean's attention back to Castiel. For a split second, no one spoke. Nothing happened. The Earth itself seemed to hold its breath.

Then their little corner of the world ended.

Castiel watched in mute horror as the green eyes that had made him so very sure his suspicions were wrong were consumed with black.

The demon smirked. "What tipped you off?"