Disclaimer: I do not own Supernatural or any of its characters. If I did, Castiel would have been in the midseason finale and I would have paid attention to the mythology the show already has.

Based off a Twitter conversation I had with fallenatic816, WickedNerdAngel, and HeyAssbutt regarding Cas's deal that's upcoming, Lucifer, and a what if scenario.

Too Late

Dean hadn't wanted this. There was no way in all of Hell, Heaven, and Earth that he had wanted this.

It was too late though, but hindsight was 20/20.

He remembered how Crowley had shown up at his door, while the hunter was still reeling from his encounter with Amara, and informed him that Sam was back in the Cage with Lucifer.

Dean would admit that he had panicked a bit, as well as had been a bit pissed off. After all, Sam had promised that he wouldn't go through with it until he had gotten back, that he would call Dean before he did anything. Sure, Dean had ignored his call, but he'd been a bit busy dealing with Amara. Sam could have easily waited as it wasn't exactly that urgent.

Overwhelmingly though, all that had occupied his mind was the thought that SAM IS STUCK IN THE CAGE WITH LUCIFER!

Of course, it was that thought that had sparked remembrance.

There was one being that they knew who had been to the Cage and back, one who had actually rescued Sam from there before, albeit with a minor screw-up.

Dean had no clue why they hadn't thought of the angel earlier. It would have been a lot better to talk to him about this than go to Crowley or Rowena.

Castiel, understandably, had been furious.

"Why didn't you consult me?!" The angel had stared at Dean incredulously. "Why didn't you even ask me about these visions? It was fairly clear that they weren't from God."

"Look, Cas…" Dean had held up his hands placatingly, but Cas turned away from him, pinching the bridge of his nose like he was developing a headache. "Look," Dean said more forcefully, "you've had a lot on your plate lately, and…"

"That is no excuse." Cas whirled back to him, anger flaring in his eyes. "You've simply been having me search for more lore on the Darkness, none of which has been remotely helpful. Have you simply been trying to keep me away?" There was a slight tremor in the angel's voice at that question.

"No." Dean replied. "It's just with Amara, there's…" He trailed off, unable to explain what was going on between him and the Darkness.

Castiel just stared at him, and for the first time in a long time, Dean couldn't read him. With a sigh, he had sat down at the table, his head bowed down to fall into his hands.

Dean had never seen the angel look so defeated.

"Do you truly believe that Lucifer has a role to play here, despite the fact that the visions were a lie?" Cas asked.

Dean hesitated, but then he answered as truthfully as he could.

"Well, you know as well as I do that only the archangels and God were really around when the Darkness was last up and about, and they helped seal her away. Sam thought he might know something or even help." Dean said.

Cas gave a small nod. "He is known as the Light-bringer." He fell silent, looking off into the distance. For a moment, it was like Cas was seeing something that Dean wasn't.

Dean had only been able to stare at him, a strange sense of unease overtaking him. "Hey, Cas, are you alright?" There had been something off about the angel.

Castiel had stood and straightened his spine like the soldier he was. "I will deal with this." He stated, his conviction shining through. He took the laptop and pulled up the address of a near-by motel. "Meet me here."

"Cas – " Dean had reached out, but to his surprise, Cas had flinched away.

"Don't." The angel had softly said, and with a swish of his trench coat, he'd walked up the stairs and out of the Bunker.

Dean had done what he'd been told, renting a room at the motel just like he and Sam always did while on a case. He didn't know why Cas wanted them to move to a different place, as the Bunker was the safest place for them, but he had practically seen the hamster wheel turning in Castiel's strategic brain so he did what he was told.

And it had been worth it when Castiel had shown up, Sam in tow.

For a moment, things had been perfect, though only because Dean hadn't noticed.

He hadn't noticed the way Sam was looking at Cas in horror and guilt. He hadn't noticed the slump of Cas's shoulders, the distant gaze as Dean had run up and hugged his brother. He hadn't noticed that considering that Cas had obviously had a hard time the last time he'd visited the Cage, a hard enough time that he hadn't noticed that he'd forgotten Sam's soul, this had been way too easy. Especially considering that Cas's wings were broken so he couldn't just try to flit in and out.

It hadn't mattered, because Dean had his brother back.

Until now. Now when he finally noticed something was wrong.

With a cry of pain, Castiel doubled over. His breaths came out in pants as he fell to his knees on the ground and curled around himself, clutching his chest as if it was hurting him.

Dean drew back from Sam. "Cas?!" He hurried over to his friend. "Hey, what's wrong?"

"Dean…" His name leaked past Cas's lips, filled with pain. A trembling hand reached out to the hunter and he immediately took it.

"Cas, hey, it's okay." Dean gave his hand a gentle squeeze. "I'm not gonna leave you… Just tell me what's wrong and we'll fix it. Did you get injured or something?"

"Sam…" Cas's eyes dragged open slightly, looking past Dean towards his brother. "You both need to get out of here."

"What?" Dean looked between the two, and he finally took note of Sam's guilty expression. "What's wrong?"

"He's coming. You must go." With that, Cas pulled his hand away, but Dean snatched it back.

"No!" Dean yelled, feeling a bit angry with both of them. What had they done now? "Who's coming?"

"Lucifer." Sam murmured, appearing slightly terrorized at the prospect, but his guilt didn't abate as he looked at the angel.

"Lucifer?!" Dean became aware of a high-pitched buzzing and it was getting stronger. He knew that sound.

An angel's true voice.

"What did you do?" He demanded.

"I saved your brother, just like you wanted. Just like you always want." Cas managed to lift his head to look fully at the hunter, and Dean felt shock run through him at the complete anguish in the angel's face and eyes. "You need to leave."

With the last of his strength, Cas managed to push Dean away. A bright light was appearing around them, and it was giving him the willies.

"Wait!" He reached out towards the angel, but Sam pulled him away.

"Goodbye, Dean." The words were quiet, filled with guilt, pain, and something else that Dean couldn't place. The last thing he saw was Cas's pained, blue eyes before the buzzing reached a crescendo as the light flared and both Winchesters had to look away.

Somehow, Dean knew that image would would haunt him for a long time.

As suddenly as it came, the light disappeared. In its wake, it left Castiel crouched on the ground, though he no longer appeared to be in pain.

The angel slowly stood up and he studied his hands as if he'd never seen them before.

Both brothers lowered their arms which they had used to shield their eyes from the light.

"Cas?" Dean asked trying to take a step forward, but Sam held him back. He sent a glare at his brother, but Sam's eyes never left Cas.

"That's not Cas." Sam said quietly to Dean. "Not anymore."

"What the hell are you talking about?" Dean spat at him. "Of course, it's Cas. Who else–"

At that moment, Cas began to laugh, and it sent chills down the hunter's spine. He turned and stared at the angel, because that wasn't Cas's laugh. It wasn't that small huff of air or even the occasional small chuckle that was the closest the angel ever got to a full laugh. There was something familiar about it though.

"Ah, little, itty-bitty Cas sure is something." The thing that looked like Cas said, watching his flexing fingers. His voice was higher than Cas's but lower than Jimmy's. "So willing to sacrifice himself. I haven't had such an easy time cutting a deal since Cain and Abel." With that, the thing looked up fully and caught Dean's eyes with a crooked grin. And as he stared into those flat eyes that were normally the bluest thing Dean had ever seen and lit up with the angel's emotions, it hit Dean who this was.

"Lucifer." Dean growled, stepping up to protect Sam from the archangel. At his words, lightning flared, revealing the whole angel wings in his shadows. "What are you doing in Cas? Get the hell out."

Lucifer tilted his head in a mockery of Cas's familiar gesture. "Get out? No can do." He grinned. "It's part of the deal."

"What deal?!" Dean demanded. "Cas, what the hell did you do? Why?"

"To save me." Sam said quietly, and the older brother turned to see him fidgeting in guilt. "Lucifer would leave me alone and release me, but Cas has to be his vessel instead."

"Is that – " He glanced between the two. "Is that even possible?" After all, part of the big deal of the Apocalypse was that Lucifer and Michael had needed him and Sam specifically.

"Oh, it's possible all right." Lucifer ran his hands over the body he occupied, seeming to enjoy the glare that Dean sent him in return. "Maybe not if this was the original body, but this is a vessel created by Daddy dearest specifically for Cassie in the image of his original one."

"Why? Why did he do this?" Dean felt like he was teetering on the edge, and if something didn't change soon, if he didn't regain his equilibrium, he was going to fall.

"Well, let's see." Lucifer paced back and forth, those familiar yet unfamiliar blue eyes never leaving the hunter. "As much as you don't like to admit it, you need me in order to stop our dear Aunt. To do that, I need to be here, not the Cage. Plus," his gaze moved to Sam over Dean's shoulder, "everyone knows that the only person you really care about is your brother, so he's ensuring his safety."

"And Dean's." Sam cut in.

"Ah, yes. That was part of the deal, wasn't it?" The archangel said contemplatively, tapping a finger to his chin. "The deal was that he'd be my vessel in exchange for your release, help against the Darkness, and an unbreakable vow to not harm either Winchester. I can't even lay a finger on a single hair." He shrugged. "Still, one of the best deals I ever made. Though I really thought it'd be you who showed up at my doorstep, not your pet angel." At this point, he looked directly at the elder Winchester.

Dean blinked. Cas had wanted to ensure not just Sam's safety, but his own? That still wasn't going to fly, no matter how surprised the hunter was. "Yeah, whatever." He grabbed his angel blade from his belt and held it loosely in his hand. "Get out of him; break the deal." Dean ordered.

Lucifer didn't look the least bit intimidated. "Such obvious anger over his loss." He commented lightly. "Castiel probably wouldn't believe that you're capable of showing such care for him, even if he did have any awareness of what was going on."

Dean paused. "What?" He asked, a bit horrified. Why on Earth would Cas even think that?

"Ah, yes. Poor, little Castiel. Unloved and unwanted." Lucifer laughed. "He doesn't think anyone cares, and from what I've heard it's mostly right. At most, he thinks that everyone treats him as a convenient tool. Even you guys." He gestured at the Winchesters. "I mean, did you even realize he has what you humans call PTSD?"

Both Winchesters jerked at the revelation, and shared a glance. "Cas has PTSD?" Sam asked incredulously.

Lucifer barked out a laugh. "Neither of you noticed? No wonder he thinks you don't care!"

"Cas would have told us!" Dean insisted, but there was something in the back of his mind that said that statement didn't ring true.

"Of course, he wouldn't! He would never want to burden you with his problems." Lucifer sneered, and it was so weird to see such an expression on Cas's face that was usually so kind and gentle unless one of the Winchesters was threatened. "But you guys didn't even notice how he didn't want to leave the Bunker. You didn't notice how he was having flashbacks of Dean here pounding in his face under the influence of the Mark, while every nasty thing that he's ever been called or told was ringing in his head. Or how he has flashes of him beating Dean and wants to curl up into a ball and die for hurting him. He was suffering and you guys didn't even give it pause. What'd you do instead?" He laughed as if it was the funniest thing he'd ever heard. "You yell at him when he doesn't do exactly what you want, when all he was really doing was avoiding being manipulated once more."

Dean's veins felt like they had been dipped in ice. Had he really been that ignorant to someone he thought of as his best friend, that he claimed to be family? Sure, the Darkness had been weighing on all their minds, and Cas had been putting in more effort than anyone to find out how to stop her, but was that really excuse for once again not seeing that Cas was in pain?

No, it wasn't an excuse.

"So, overall, it makes so much sense that he was willing to make a deal with me. He doesn't value himself at all, so why shouldn't he sacrifice himself for two muttonheads that barely acknowledge his existence lately?" Lucifer shrugged, happily taking in how uncomfortable and guilty the Winchesters were. Then, a thought seemed to occur to him, and his posture immediately shifted. He gave a sad sigh. "So much care you're showing, Dean, for him and he'd never believe it. It's such a shame, too… He loves you, you know."

Dean felt like he'd been hit by a semi again, all he could do was stare at the archangel in his best friend's body.

Cas loved him? They were friends and family, sure, but Lucifer didn't seem to be implying that.

If what he said was true (and this was coming from the King of Lies), then Cas didn't love him, he loved loved him.

That couldn't be true. If it was…

"Oh, well." Lucifer grinned and his expression reminded Dean of that time that Cas had been possessed by Leviathan. "Too bad you'll never see him again."

Dean snapped. "Leave him alone, you sadistic son of a bitch!" He tried to pretend that he didn't hear the half sob in his voice.

Lucifer smirked and positively sauntered over to Dean. He leaned right into the hunter's personal space. "You don't get it, do you, you worthless insect?" There was a malevolent glint in his eye. "He did this for you, you know. It's always been for you." He leaned back, but he stayed close, again mimicking the angel's normal space issues. "That's why he asked for this."

Dean stepped back like he'd been slapped. No, Cas couldn't have done this for him. He hadn't wanted this. He would never ask for this.

"And I'm never going back." Here Lucifer flashed him a shark-like smile. It made it quite clear who, despite managing to force binding promises to protect the Winchesters and the world, got the short end of the stick in this deal.

"No. No, that's not…" Dean muttered helplessly, mostly to himself. He was still reeling from the fact that Cas had probably done this for him. It wouldn't be the first time after all that Cas had made momentously bad decisions and then said it was to protect him (even if it backfired). But his motivations for it…

"How could…" Dean couldn't even get the question out. He looked back at Sam, hoping to see the same confusion he was feeling. He was disappointed in that regard.

Sam was looking at him with a mixture of pity and sympathy on his face. It was the same face that he used on family members of victims.

He turned back as Lucifer laughed again. Dean sent the archangel a glare that, if he were Superman, would have burned the archangel to a crisp. "Should have treated him better when you had the chance." Genuine mirth shone in Lucifer's eyes at the pain he was causing.

With a growl, Dean took a swipe at the archangel, but he just danced out of the way and laughed, blowing a mocking kiss in his direction.

"Ah, ah, ah." He chided. "Loverboy's still in here, you know. Kill me, and you kill him. Also, you'll be losing your greatest chance against the Darkness."

Dean stiffened, because Crap! Lucifer was basically holding Cas hostage, and there was nothing he could do about it. It had taken all that Sam had had to throw off Lucifer's controlled when the archangel possessed him, and Cas hadn't been in top form for a long time to even begin to attempt to stop the guy.

"You know," Lucifer again said contemplatively, following his earlier track and cocking his head to the side. "You also shouldn't have kissed our aunt."

Dean's stomach plunged to his feet, and he could almost feel Sam's judgmental gaze on him. "You know about that?"

"There were angels present. It was all over angel radio." Lucifer snickered. "Seems it made Cassie here even more depressed. After all, you kiss and defend someone going around and killing people during a tantrum, but you won't look twice at him."

"No, that's not – " Dean spluttered, wanting to explain. Except the one he wanted to hear it wasn't even aware of anything going on.

"Well, I've got my bargain to live up to. Have a nice life, Winchesters." With a final evil sounding laugh, the archangel flew away with the sounds of fluttering feathers.

"No!" Dean was reaching out to grab something that was already gone. "No." He said more quietly, falling to his knees as he stared at the spot where Lucifer had taken his best friend away from him.

He wanted to scream, he wanted to shout "No!" from the top of his lungs like that iconic Star Wars scene. All he could get out was that soft, sad "No." though, like from Star Trek when Kirk had faced Spock's death on the other side of the glass.

His hands curled into fists as he clutched at the ground.

"Did you know?" He asked quietly.

"Know what? About the deal? I was there when he made it, Dean." Sam said, his voice a mix of bitterness and guilt.

"No." Dean said. "Did you know about Cas's feelings?"

There was a long moment of silence that spoke volumes. The answer was all too clear.

"Why didn't you – " Dean growled.

"Why didn't I tell you? I didn't think I had to." He felt more than saw Sam sitting next to him. A tentative hand fell upon his back in a gesture of comfort.

Dean shook off his brother's hand and glared at him. "Well, apparently you did! How the hell was I supposed to know that Cas liked– that he lov–" He couldn't even say it.

Sam's face crinkled in sympathy. "Because everyone else could see it." Dean stared at him, incredulously. "How many people have pointed it out, to your face, that Cas had feelings for you? It was obvious how he felt."

Now, that he mentioned it, he could see that Sam was right, but he'd always brushed it off. Angels, demons, Crowley or whoever were just trying to get a rise out of them. He never thought that they were serious. And this all had been going on since practically the day they met.

"Goddammit!" Dean cursed, letting his head fall into his hands.

How could he have not noticed Cas's feelings? How could he not have seen how Cas was suffering because of all the crap they'd been through? How could he have not tried to help the angel?

Becoming wrapped up in his own problems wasn't much of an excuse. Cas was his best friend; he was supposed to be family, and family took care of each other no matter what.

Even more importantly, Cas was the person that Dean loved.

Dean had failed the angel once more. He'd let him fall and he hadn't been there to catch him, and now Cas was gone.

And so Dean was falling, too.

"Hey, we can fix this." Sam tried to be optimistic.

Suddenly, Dean wanted to snap at his brother as he looked up to send him a glare, because this was his fault. It was him who decided to remove the Mark when Dean had said no, thereby releasing the Darkness. It was him who decided to talk to Lucifer because of some stupid visions and gotten himself caught, meaning that Castiel had had to make the deal to save him.

Because Cas didn't value himself and thought that Sam was the only person Dean cared about.

And just like that, Dean's anger deflated as it all came full circle.

The older Winchester hunched in on himself. "I don't think we can this time." He said weakly, bringing his hand up to cover his eyes.

Because Dean had known from the moment Lucifer looked up and he hadn't seen even a spark of the angel.

Still within the archangel or not, Cas was gone.

It was too late.

AN: So this started as someone made a poll on Twitter about whether or not people would like to see Misha as Lucifer (as in Cas gets possessed by the archangel), which 52% voted yes for BTW. This also came into play because Misha said that Cas is going to make a really bad decision soon (a proverbial deal with the devil), so with Sam in the Cage, it didn't seem like such a stretch. In any case, some of us then created some back and forth dialogue in which Lucifer as Cas tells Dean that Cas loves him and did all this for him and Dean reacts (that dialogue is part of the above conversation though I added in more). After asking if I could write a fic off it, I wrote this. It's a real possibility, I think, and since it's been shown that angels can access the memories of those they possess, I totally think Lucifer would drag up all the pain Cas has been hiding and how he feels, just to make the Winchesters hurt. I also tried to fill in the plot potholes that the midseason finale had. Anyway, I hope you liked this.