A/N: So I never wanted to touch a season 6/7 fic because I hated Cas going dark side. But I guess my muse decided I needed a challenge, so this fix-it came about. I'll warn you, it's going to be very painful before there's a resolution. Huge thanks to 29-pieces-of-me for suffering through beta reading it! No slash.

Side note: Thank you so much guest Jaz for your kind words over on Gone Nuclear. I love hearing what my readers think and every review always makes my day. ^_^

Disclaimer: I don't own Supernatural, or the lines lifted from seasons 6 and 7.

Chapter 1: Mistaken Identity

Dean and Bobby carefully made their way into the building where Cas and Crowley were poised to pop Purgatory. An angel killing sword was in Dean's hand, and he was mentally preparing himself for having to use it. Cas had gone off the deep end, and Dean had to do everything within his power to stop the angel, even if that meant killing him. And since Cas had taken down Sam's wall and left him in a friggin' coma, Dean didn't think it'd be all that difficult for him to do.

He entered through a door at the top of a set of stairs leading down to a laboratory, but the sight that greeted him wasn't exactly what he'd expected. Crowley was there, reciting an incantation in front of a blood sigil painted on the wall. But Cas was nowhere to be seen. A black woman stood next to Crowley instead, and the hair on the back of Dean's neck stood on end—he had a strong inkling as to who that was.

He didn't have time to wonder where Cas was in all this, for the spell would be complete soon and Purgatory opened. Standing at the top of the stairs, Dean arched his arm back and threw the angel blade at Raphael's back. Without turning around, the archangel whipped his hand around and caught the blade before it could pierce his vessel. Dean silently swore as Raphael and Crowley turned to look at them. Then he felt an invisible force punch his chest and propel him down the stairs. He landed on a table with a hard thud before dropping to the floor. Bobby tumbled into a heap a few feet away.

"Bit busy, gentlemen," Crowley said. "Be with you in a moment."

Dean groaned, rolling onto his side and grimacing as his back spasmed. Shit. Raphael now had his only weapon against an angel. He vaguely heard Crowley finish the spell, and Dean's heart stuttered with a profound sense of failure. But then he noticed that nothing had happened.

"Hm, maybe I said it wrong," Crowley mused.

There was a flap of wings, and Dean caught a flash of tan trench coat in his peripheral vision.

"You said it perfectly," Cas said. "All you needed was this."

Dean pushed himself to his feet as Cas set an empty jar stained with blood on a cart. No…

"I see." Crowley walked to the wall and touched the blood painted there. "And we've been working with…" He tasted it. "Dog blood. Naturally."

"Enough of these games, Castiel," Raphael snapped. "Give us the blood."

Crowley snorted in disbelief. "You- game's over. His jar's empty." He turned back to Cas with mild curiosity. "So, Castiel, how'd your ritual go? Better than ours, I'll bet."

Cas closed his eyes, and then suddenly began to glow. The light grew in intensity until Dean and Bobby had to throw their arms up to shield their eyes. Dammit, they were too late!

The light faded, and Dean had to blink spots from his vision. Crowley and Raphael looked just as disoriented by the show.

"You can't imagine what it's like," Cas spoke, voice sounding far too calm and awestruck than the situation warranted. "They're all inside me. Millions upon millions of souls."

"Sounds sexy," Crowley replied, and in the next instant he'd disappeared.

Dean wished he and Bobby could do the same. Standing on the sidelines while two juiced up angels had a nuclear showdown was not something he wanted to partake in. Raphael actually looked frightened, which wasn't all that surprising considering Cas looked frightening. There was an otherworldly glow to his skin, a lingering silhouette after that brief display of power from all the souls he'd ingested.

"Now what's the matter, Raphael?" Cas taunted. "Somebody clip your wings?"

Raphael's brow furrowed, and his gaze narrowed shrewdly on Cas. Then the vessel's eyes flew wide in what seemed to be shock mixed with a glimmer of…joy? Raphael took a tentative step forward, hand reaching out, not to smite, but as though to embrace Cas. Dean exchanged a bewildered look with Bobby.

"Brother, is that you?" Raphael gasped hopefully. "What are you—"

Cas snapped his fingers, and Raphael exploded in a shower of blood and guts that splattered the walls and floor. The angel blade he'd been holding clattered on the tiles. Cas then turned his head to Dean and Bobby, expression carefully neutral.

"O-kay, Cas," Dean finally managed to stammer. "You did it, you defeated Raphael. Now let's defuse you, okay?"

"No," Cas replied somewhat sharply. "The souls belong with me. I still have work to do."

Dean's stomach clenched. "No, Cas, it-it's scrambling your brain. You don't need this kind of juice anymore. Get rid of it before it kills us all."

Cas rolled his eyes. "Here Castiel saved you, and yet you can't manage even a modicum of gratitude. It's astonishing, really, why he stayed devoted to you at all."

Dean frowned. What the hell…was this like a punch-drunk Cas referring to himself in the third person? "Listen to me! Listen, I know there's a lot of bad water under the bridge, but we were family once—" He cut off in stunned surprise as Sam stumbled into the laboratory and picked up the fallen angel sword. Dean wanted to shout at him not to do it—he'd thought he could, thought he could kill Cas without compunction, but instead Dean found himself desperately wishing that he could simply talk Cas down…but if the angel wouldn't listen…dammit, they couldn't let him destroy the world.

"Cas, please." Dean wasn't above begging, not for this.

Cas's next words cut through him like a razor from Alastair's rack. "You're not my family, Dean. I have no family."

Sam lunged, driving the angel blade into Cas's back. Dean turned away to avoid the resulting flash of light, but none came. When he looked back, Castiel casually pulled the blade out and put it down. There wasn't even blood on it.

"I'm glad you made it, Sam. But the angel blade won't work because I'm not an angel anymore. I'm your new God. A better one. So you will bow down and profess your love unto me, your Lord. Or I shall destroy you."

Dean's mouth dropped open. He had to be friggin' kidding!

For a long moment, nobody moved, and then Bobby slowly started getting on his knees. "Well, all right then. Is this good, or you want the whole 'forehead to the carpet' thing?" He shot Dean and Sam a pointed glare. "Guys?"

"Cas, come on," Dean pressed. "This isn't you."

Cas's stoic face broke into an uncharacteristic grin then; Cas's smiles were always subtle and slightly awkward, but this was an almost crazed, exhilarated beam. He shook his head in amusement. "That's true. So I suppose there's no reason to keep up the charade anymore." He began to pace casually, and Dean felt a whole new sense of unease. This wasn't right. Cas was always so still, having not perfected human mannerisms even after three years hanging with the Winchesters.

"Who are you?" Dean demanded. Some monster soul from Purgatory?

Cas—or whatever it was—smiled. "I thought you'd instinctively recognize me, Dean. Though, I admit I'm not quite the same. Your darling little Sammy here can tell you that the Cage does terrible things to one's mind." The thing wearing Castiel's face lolled his head to the younger Winchester, a smug smirk tugging his mouth.

Dean's blood ran cold as that tone and that phrase rang eerily familiar. It couldn't be…

Sam backed up, eyes wide with terror. "Lucifer?" he rasped.

"No," Dean grunted, gut turning to lead. "Michael."

The archangel beamed at him.

Dean clenched his fists. "How? Cas popped Purgatory, not Hell."

Michael laughed. "Oh, I've been back much longer than that, Dean." He flicked his gaze toward Sam again, and Dean hated the way the archangel was positively gloating. "You see, Sam, when Castiel raised you from the Cage, he thought you were intact. He didn't realize that the little spark of soul he cradled so protectively was actually grace. Dimmed down and subdued to mimic a frail, human soul. And with how fiercely he guarded that piece when he flew out of Hell, it was easy to slip past his walls and latch onto him instead."

Sam could only stare in horror, which was exactly how Dean felt. How could this have happened? How could he not have noticed over the past year that Michael was riding around in Cas?

"No," he growled. "You're not that good an actor. All the times Cas came to help us, that wasn't you."

Michael shrugged. "True. I couldn't take full control right away. At first, I merely bided my time. Raphael was going to destroy Castiel anyway, and then we could restart the Apocalypse." He paused, mouth curving upward. "But then the most intriguing thing happened—a demon came to Castiel with a proposition."

"So, what, you got on the pop Purgatory band wagon?" Dean snarled.

"No. I accepted it." Michael let the implication hang in the air for a moment. "Castiel was going to refuse; I saw it in his mind. He wanted to go to you for help instead, even though it pained him to bring you back into the battle." The archangel sneered in disgust. "That was the first time I surfaced. And steadily more often as time went on."

Any retort Dean had disintegrated like wax on his tongue. He'd accused Cas of not coming to him for help, of choosing a demon over them. Cas hadn't denied it, but…how much of the past few days, hell weeks, had Dean's conversations with the angel really been with Michael? Dean's and Cas's friendship had been strained this year, and Dean had spent a good deal of time being pissed at the angel. What if his anger had clouded his perception? What if when he accused Cas of being a dick, it'd been Michael instead?

"Why'd you kill Raphael?" Bobby spoke up gruffly when it seemed neither Winchester was going to say anything. At least he'd gotten up off the damn floor. "Weren't you two bosom buddies?"

Dean felt another revelation punch him in the gut. Raphael must have recognized Michael in those last moments. But if Michael hadn't intended to keep up the act in front of the Winchesters, why kill the other archangel?

"Time in the Cage has a way of…changing one's perspective," Michael replied, and there was a brief flash of darkness in his eyes. "I tried to be the good son, do what was right and expected of me. It was all supposed to turn out a certain way." His voice had grown softer and more distant, but then it flared to life again as Michael raised his head. "My father is long gone. So instead of his version of paradise, I decided it was time to make a new one."

"You're saying Cas wasn't working with Crowley?" Sam joined the conversation, sounding breathless and unsteady.

"Didn't know a thing about it. Death isn't the only one who knows how to put up walls."

Dean's heart dropped into his stomach. "You took down Sam's wall," he whispered.

Michael cocked his head, but it was nothing like Cas's inquisitive or confused mien, just pure superiority and arrogance. He smirked at Sam. "Enjoy the hallucinations that are to come, Sammy."

Dean stiffened. What? Fury erupted in him like an atomic bomb, and he almost charged the douchebag wearing his best friend's face. "You son-of-a-bitch. Cas! If you're in there, you have to fight him!"

Michael angled a forbearing look his way. "He can't hear you, Dean. But even if he could, I doubt it would do any good. The last memories he has of you all is trapping him in a ring of holy fire and leaving him there as a cloud of demons descended."

Dean sucked in a breath. "What?"

Michael grinned. "I let him catch a few crucial moments. Oh, like just now with Sammy stabbing him in the back. Castiel currently believes he's dying from that blow after his beloved Winchesters left him in this cold, dark place. Alone."

Sam's face drained of color. Dean's own chest was getting too tight to breathe properly. This couldn't be happening.

"Well," Michael said jovially. "I have work to do. I hope for your sake this is the last you see of me." And with that, he disappeared.

Dean staggered forward, arm raised halfway as though he could grab an invisible wing and bring Cas back. Cas, who he'd thought had betrayed them, who he'd thought had intentionally hurt Sam by bringing down the wall. But Cas hadn't done any of those things. He'd been locked in his own head—still was. Just like Sam.

Bobby cleared his throat. "What do we do now?"

Dean looked up to meet the older hunter's eyes, then glanced at Sam. He frowned when a trickle of blood starting streaming from Sam's nose. Dean's heart rate spiked. "Sam, you okay?"

Sam let out a choked gasp and fell to his knees, cutting his hand on a jagged piece of broken glass. Dean and Bobby darted over, just as Sam let out a garbled scream and squeezed his eyes shut. Dean grabbed his shoulders, shouting his name, but then Sam fell limp in his arms.

"No, no, no, come on Sam!" Dean shook his brother.

Bobby gripped his wrist to stop him, his expression compassionate yet stern. "Let's get him home."

Swallowing hard, Dean nodded and helped Bobby lift Sam from the floor. Helplessness began spreading through Dean's limbs, sweeping in with a numbness he was all too used to feeling—and hated. He'd lost Lisa and Ben. He'd lost Sam. Now he'd lost Cas too. And Dean couldn't help but think that it was somehow his fault.