"Get out of him now." Dean growled.

The demon stared expressionless at Dean. The voice that came out of Sam's mouth was weak. "Can't."

"Uh uh. 'Can.'" Dean corrected. He pulled out the demon blade. "Do it. Now."

"If I could, I would." The demon rolled Sam's eyes. " I'm dying, you moron. Your dumbass brother had to have that stupid ink on his chest and mess everything up."

Dean shook his head on confusion. "What are you talking about?"

Sam's eyes blinked back to hazel. He opened his mouth but before he could speak his whole body convulsed. Dean started towards him but halted as Sam's eyes reopened, black as night. The demon started, then laughed humorlessly. "Sam's practically gone, and he's still fighting. Gotta give him credit, he's not giving up."

"And you?"

Another laugh. "Oh, I've given up. I may be dying, but at least the pain has stopped now that Sam finally ripped off that abomination." He shrugged casually. "Not the way I wanted to go out, but at least I'm taking a hunter down with me."

"We'll see about that." Dean ran to the final group of symbols and took out all his rage, all his fear on the wall. A huge chunk of concrete fell to the ground with a large crash and a wave of light rose up from the ground and continued up past the ceiling as the spell lifted.

Dean screamed out Castiel's name, then fell forward as something smashed into his back. Rolling over he saw Sam on his knees next to him, the demon blade in his hand. Black eyes glared hatefully as the demon plunged the knife towards Dean's heart. Dean managed to catch the arm with his hands and tried to keep it away from him. The demon was fighting for its life, its enraged yell echoing in the dark basement as it inched the blade closer and closer to Dean's chest.

Next thing Dean knew Sam was jerked backwards. Dean gasped and sat up. A very confused looking Castiel stood over him with Sam's crumpled body behind.

"Dean, what is going on?"

"Sam's possessed! He's dying! Move!"

To his credit, Castiel didn't pause for even a second to try to figure out what he was dealing with. The demon tried backing away from the angel but its strength was gone. Cas knelt down on one knee, grabbed Sam's shoulder and put his other hand on his head.

Sam's head whipped violently back and black smoke slowly tricked from his mouth. Wisps of smoke lazily rose out of Sam's wounded chest. Cas readjusted his grip on Sam's shoulder and pressed harder onto the young Winchester's forehead. The smoke started coming up from the surrounding skin then abruptly reversed course and went back into Sam.

Cas let go with a gasp and reeled backwards. He looked back and forth between the brothers in confusion.

"Dean, I can't... what is this?"

"I don't know!" Dean shouted. "The demon's bonded to him or something." He looked at Sam's still body in horror. "He's not breathing, Cas, come on!"

Cas rolled up the sleeves of his trenchcoat and knelt down in front of Sam, grabbing both sides of his head as Sam's eyes flew open.

Both men threw back their heads as black smoke began pouring out of Sam's chest his eyes, his nose, his mouth, his skin, even the top of his head. Dean shouted in triumph. It was working! Finally all the smoke came out of Sam and hovered in the air a moment before slowly dissipating.

Sam fell back and went still. Dean flew over, praying it wasn't too late. Dean felt but found no pulse.

Dean screamed for Castiel to hurry, Sam was dying! Cas looked a bit dazed from the draining exorcism but pushed himself back to the Sam's side. He laid one hand back on his forehead and one over the ripped skin by his heart. A soft glow emanated from under his hands and he worked to repair the extensive damage Sam's body had endured over the last few hours. Dean held on to his brother's hand and pleaded over and over, "Cas, come on! Sam, please!"

After an eternity Dean saw the skin on Sam's chest pull itself back into place, the blood fading. Soon the skin on his chest was intact, although there was no sign of the tattoo. The color slowly came back into Sam's skin, and Dean expelled a breath he hadn't realized he'd been holding as he saw Sam take a shaky breath.

Cas sat back, looking exhausted. Dean looked at him questioningly, hope on his face. Cas answered the unspoken query. "He's alive. I need a minute to rest before I can finish healing him, but he'll be okay."

Dean closed his eyes. "Thank God." He used the time to go back upstairs and grab Sam's duffle bag and to make sure he had everything stowed away. By the time he was done Cas was just putting his hands back on Sam's chest.

It took a little longer than before, but this time when Cas pulled his hands away he smiled. "He's okay now."

Right on cue Sam opened his eyes. He put a hand to his chest and took a big breath. Dean grabbed his hand and looked intently at his brother.

"Sam, you okay?"

Sam looked dazed. He rubbed absently at his chest, then gave Dean a wan smile. "I think so."

Cas and Dean both took an arm and pulled Sam to his feet. Sam swayed a little and Dean grabbed his arm to steady him.

"You're still pretty weak, Sam." Cas said. "Your heart, all your organs were practically beyond repair. You're fully healed, but you do need a little time to fully recover your strength."

Sam nodded. He'd never been so tired. Weariness set deep in his bones. But his heart was beating normally. His stomach, his abdomen were all pain free. The ground beneath his feet was steady. But most importantly, his head seemed clear. He turned to Dean. "The demon?"

"Gone." Dean answered. "Pretty sure for good."

"Good." Sam sighed. "Can we go home now?"

Cas used his instantaneous angel taxi service to get them all outside the prison walls, landing the three men right next to the Impala. Sam gave Castiel a brief summary of what had happened while Dean stowed their gear. Cas shook his head as he listened.

"I've never encountered anything like that. It was hard to distinguish your essence from the demon's. It was like..." Cas broke off as he searched for the right words.

"Like trying to separate Kool-Aid from water." Sam said, almost absently.

Cas looked puzzled as he tried to work out the analogy. "I'm unfamiliar with 'Kool-Aid.' Your fever was raging. You were anything but 'cool.'"

Dean snorted, grinning as he came around to stand next to his brother. "I'll fill you in later, Cas. Right now we gotta hit the road."

Cas still looked confused but nodded. "Get some rest, Sam."

Sam's looked somberly at the angel. "Cas. You saved my life. Thank you."

"You really came through, man." Dean added.

Cas nodded back grimly. "I'm glad you're okay, Sam." And just like that he was gone.

Dean gave his brother an assessing look. "You sure you're okay?"

Sam gave a brief half smile. "I could sleep for a week, but yeah. I'm good."

Dean pulled Sam in for a fierce hug. "You scared the crap out of me."

Sam chuckled. "It wasn't exactly a day at the park for me either."

Sam settled into the passenger seat with a contented sigh. It felt good to be home.

The Winchesters checked into the first motel they came across, and both fell asleep the second their heads hit their pillows. The next morning Sam slept in while Dean went on a coffee and breakfast run. Sam was just getting up when he returned. He smiled gratefully at the steaming cup of coffee.

"Man I need this."

Dean sat on the bed opposite Sam's and took a sip of his own. "So what exactly happened?"

Sam looked at Dean over his cup and raised his brow questioningly.

"With, you know." Dean gestured at Sam's chest.

Sam frowned. He remembered the all encompassing pain in his chest, the despair, the overwhelming need to tear at his skin. "I don't really know."

"Was it the demon?"

"I don't think so." Sam answered slowly. "Maybe a little. Honestly, I just couldn't take the pain anymore. I couldn't help myself. I just had to make it stop." Sam looked down and shuddered as he unconsciously rubbed his chest.

Dean swallowed the lump in his throat. He'd been so scared, felt so damn helpless. He was the big brother, the protector, and he could do nothing to keep his brother from suffering, from nearly dying. If only he'd been the one to grab that door handle.

Sam seemed to read his mind. "Dean, there was nothing you could've done to stop it. There's no way we could've known that crap was on the door. Or that something like that was even possible." He tried changing the subject. "What are we going to do about the prison? We have to make sure no once else gets possessed."

Dean waved him away. "All set. I talked to Cas and he's going to do a bunch of purification angel mumbo jumbo stuff over there, make sure it's safe." He frowned. "Although we still don't know who did it in the first place."

"His name was Naberius."

Dean nearly spit out his coffee. "How do you know that?"

"I think as he was getting weaker, and the spell of the tattoo was also getting weaker, some information kind of came across the wall. His name was Naberius, and he created that weird demon slime stuff."

Dean frowned. Wait. So the demon that was in you, that was in the slime or something, he was the one who made it?

Sam nodded.

"How? What the hell was the point of it?"

"It was a more permanent possession, somehow. I don't exactly understand the science, but somehow absorbing through the skin merged the demon more quickly and tightly to its host."

"Kool-Aid."

Sam shot off a quick grin. "Right. Kool-Aid." The smile faded as he continued. "The people that disappeared? They were basically his failed science projects. Three of them died as he tried perfecting the stuff. The first one-" Sam broke off.

"What?" Dean prodded.

Sam shook his head. He could still see it in his mind's eye. "The first one, the slime basically ate away the skin of his hand and just kept going. It was like acid, it slowly burned him away, bit by bit." Sam shuddered. "It took hours."

Dean was shocked. "God, that's awful."

"The fourth one, Natalie Jennings. That one worked. She could feel the demon slowly taking over her but couldn't stop it. It literally drove her insane. Naberius nabbed a priest to try and exorcise the demon and it couldn't be done. Natalie wasn't human anymore, she'd become this, this thing. Like, a hybrid."

"The demon and the girl, fused together." Dean mused. "God, that's awful."

"Once he'd finally perfected it, he used it on himself and waited for the next person to come along. It was just bad luck that I was the one to touch it."

Sam took a sip of coffee, needing a moment before he continued. "The power in the tattoo wrecked havoc on him. He was bound to me, he couldn't leave, but he couldn't fully take over because of the tattoo. He was in limbo, and the longer he was in that state the worse off he became."

"But when you," Dean paused. "Once the tattoo was out of commision, he fully possessed you. But Cas was able to exorcise him."

Sam went pale. He would never tell Dean, but he remembered the exorcism. It was true, the demon had fully merged with Sam, and consequently Sam went through everything the demon endured. The previous pain he'd felt was barely a slight breeze on his skin compared to what had been happening when Castiel tried to separate them. His nerve endings had been on fire, shards of glass felt like they were ripping him apart on the cellular level.

He took another sip of coffee to compose himself, hoping Dean wouldn't notice the slight shake of his hand.

"He almost didn't. I don't know if he would've been able to if Naberius hadn't been so weak. The more he tried to take over, the weaker he got. But he had no choice but to keep attacking, trying to possess me so he could live."

Dean was shocked. It almost sounded as if Sam felt sorry for the bastard. He said so.

Sam shook his head vehemently. "No. God, no. I don't. I guess I just understand the desperation, the need to survive. He was in a battle to save his life and did whatever he could to live."

"At least one of you did."

Sam looked at Dean, shocked at the anger in his voice. "What's that mean? What, are you pissed that I wouldn't let you carve a hole in my chest?"

"I'm pissed that you gave up, that you wouldn't do what it took to survive."

Sam gaped at his brother, feeling anger bubbling up. "Are you serious? I never gave up. Not once. But I wasn't going to risk that demon taking over and killing you and God knows who else. Besides," Sam hurried on, talking over Dean as he tried to interrupt. "We don't even know if it would've done any good. It didn't really seem to once the tattoo was gone anyway."

Neither man spoke for a few minutes, lost in their respective thoughts. It was Sam who broke the silence.

"Besides, I had one huge advantage the demon didn't have."

"Oh really." Dean said, his voice dripping with attitude. "And what was that?"

"You."

Dean looked at the serious look on Sam's face. He nodded slowly as Sam said, "You saved my life."

"Well," Dean said, looking a bit uncomfortable. "Next time look where you're sticking that huge paw of yours and maybe it won't need saving."

Sam grinned.

"Deal."

END