"Please, sister, stop this," Castiel pleaded with Ariel.

"I do not take orders from you Castiel, you disobeyed, and I have no choice but to kill you," the female angel said to him. There was a deep sadness in her tone and her eyes revealed how conflicted she actually felt.

Castiel and Ariel fought, angel blades clinging together. They both knew that there were plenty of moments for one to kill the other, but neither of them wanted to make the final blow. Castiel especially stalled the fight. For a moment, Castiel allowed himself to be distracted by the sight of Sam and Dean fighting three other angels. He watched with despair as the Winchester brothers struck fatal blows into his brothers. This moment of distraction was enough for Ariel to make a decision. She sliced her blade across Castiel's arm. He yelped in surprise. The small gash stung more than usual. Cas was done going easy on his favorite sister. He took a step forward and from an outsider's perspective, it appeared as if he was embracing her rather than sliding his blade into her chest.

"I'm sorry Ariel."

"It doesn't matter. I did my job. It's too late for you." Castiel allowed himself a brief moment of mild confusion from her statement but chalked it up to her dying and whatnot.

"Goodbye, sister," he whispered sadly. Castiel was momentarily surprised by the sting of tears in his eyes. Maybe he was spending too much time with humanity. He shook it off and turned to help Sam and Dean only to find that they had finished off the remaining angels.

"Oh now you decide to help us out," Dean remarked snidely.

"Dean I…"

"Save it, I saw you conversing with your old gal pal. You know stalling like that could get you killed. I know you could have ended her faster than that. You could have helped us while we were getting our asses kicked by your angel friends, and…"

"Dean, calm down," Sam interrupted Dean's tirade. Sam was the only one to notice the cut on Cas's arm and the unfamiliar glint of tears in the angel's bright, blue eyes.

"I'm not gonna calm down Sam, he could have gotten us or himself killed!"

"I'm sorry Dean, I'm… I'm just…" Cas faltered, his eyes fell and he tried not to look at Ariel's body lying lifeless on the ground, her wings spread out and charred onto the cement.

"Spit it out Cas," Dean spat out impatiently.

"I'm just tired of watching my siblings die," Castiel whispered, his voice breaking slightly.

"Cas…" Dean tried to apologize, but Cas had already teleported away to God knows where.

Sam glared at Dean, "Did you have to be that hard on him?"

Guilt clouded Dean's face as they climbed into the Impala and drove back to Bobby's house.

Cas landed softly on a grassy field in an empty park somewhere in east Texas. He always seemed to find himself in parks like these when we was feeling particularly upset. But right now he didn't just feel upset, he felt nauseous – an unfamiliar feeling for the angel to have. A thin sheen of sweat coated his forehead as heat seemed to rise in his body.

Castiel's thoughts of his own personal well-being were pushed aside however. He thought about how he could have gotten himself or even Sam and Dean killed by stalling Ariel's death. He thought about all of the siblings he had lost to this hopeless war. He thought back to when he and Ariel were just fledglings together, how they learned how to fly together, how they learned how to take care of their wings together, and how they fought side by side as soldiers in God's army together.

Then he thought about the sharp pain in his arm. It hadn't healed yet. He snapped his fingers and fixed the tear that cut through his beloved trench coat and subsequently the suit jacket and white dress shirt. He focused on putting his grace towards the cut, but it didn't seem to be working. He exhaled in frustration and tried to ignore the irritating sting from his sister's angel blade.

Castiel's thoughts were interrupted by his cell phone ringing in this pocket. He looked to see Dean's name plastered on the screen. He pressed the decline button, spread his magnificent wings, and took off into the sky. Despite the freeing feeling of his wings slicing through the air, Castiel just couldn't shake a dizzy spell that had seemed to overtake him.

Three Days Later

Sam and Dean sat across from Bobby at the breakfast table in Bobby's kitchen. Sam, was characteristically doing research on a potential case while Dean and Bobby ate their breakfast. Dean's thoughts bounced back and forth from the case they were thinking about taking and how he had left things with Cas. He hadn't meant to be so harsh with him, especially after he had just killed his sister, but he was just worried that Castiel's good intentions would get him killed someday. Dean then proceeded to think about how ironic his worries for Cas were.

The three men were shaken out of their separate thoughts by a loud crash coming from the living room. Sam, Dean, and Bobby were on their feet in an instant with shotguns in hand.

"Who's there?" Bobby called out. As the three of them turned the corner, they dropped their weapons in shock. Castiel was laying on Bobby's carpet, soaked in sweat and breathing heavily.

"Cas!" Dean ran to Cas's side first and was instantly followed by Sam and Bobby.

Dean grabbed Cas's arm to pull him up but instantly let go when Cas yelled out in pain.

"Cas, buddy, what's wrong? What happened?" Dean questioned frantically.

"The knife… it must have been laced…"

"What knife? What was it laced with?"

"Ariel… her angel blade… it must have been laced… laced with demon blood…" Cas panted laboriously.

"What do you mean? Did she cut you? Cas this was three days ago? What the hell?"

"When we were fighting those angels, I saw Cas was bleeding. He had a cut in his arm. I figured he would heal it. Oh my God Cas, I'm so sorry I didn't ask about it," Sam stated, a look of recognition mixed with horror on his face.

"I'm sorry… I came here… I didn't have anywhere else to rest. I can't go home. I… I just need to take a few hours to rest and I'll… I'll be out of your way."

"Now son if this happened to you three days ago and you have only gotten worse then I think this is going to take more than a few hours to heal. And boy you ain't leavin' this house til you're fully healed," Bobby chided.

Cas didn't respond. It looked like he was concentrating very hard on not passing out and/or screaming in pain. Sam and Dean gently pulled him up to his feet and they worked together to pull off his layers so as to get a better look at the wound. After gently maneuvering the long-sleeved dress shirt off of him, the brothers gasped at the dark gash across Castiel's bicep. The wound was about 3 inches long and very deep. Black liquid oozed out of the wound along with some of Castiel's own crimson blood. The veins surrounding the gash were starting to turn black. Sam immediately grabbed a medical kit and began dressing Cass's wound.

"Why hasn't your grace healed this?" Dean asked.

Castiel swayed on his feet and said "Demon blood… it's poisonous to angels…"

"Can it kill you?"

Again, Castiel didn't answer as he was beginning to lose his battle with consciousness. His eyes fluttered open and closed and he would have fallen backwards if Sam and Dean hasn't caught him and gently laid him on the sofa.

"Well that's not a good sign," Bobby stated.

Shortly after dressing Cas's wound, the boys dragged him up to Dean's bedroom and laid him on the bed. They put him in one of Dean's old AC/DC shirts and laid some heavy blankets on him. He was still unconscious and he was shivering. Dean pulled up a chair and sat by his side, distress lining his features. Cas looked so much smaller and so much more fragile than the first time Dean had ever seen him. Dean remembered how he had been intimidated by the angel when he first appeared to him in that barn, with his wings spread out and his coat peppered with bullet holes that Dean had put there in the first place.

Dean placed his hand on the angel's forehead. He was burning up. "Sam we have to get his fever down," Dean said just as Bobby walked into the room with a cool towel. They placed it on Cas's forehead and watched him as he continued shivering underneath all the blankets they had on him. Bobby eventually went downstairs, presumably to make some soup or do some research.

"I know what you're doing Dean," Sam said softly to his brother.

"Oh yeah? What am I doing?"

"You're blaming yourself."

"Well if I hadn't yelled at him, he wouldn't have disappeared for three days and he would have come to us sooner. Now he could be dying and… and… I don't know what to do."

"Dean, it's just as much my fault as it is yours. I actually saw him bleeding and didn't even bother to ask if he was okay."

"Stop it Sam. Stop trying to make me feel better about this. You figured his grace would heal it."

"I'm just saying that you shouldering the blame for Cas's condition isn't going to make him better."

"Alright," Dean said begrudgingly, but Sam knew that Dean wouldn't stop blaming himself no matter what he said to him.

"I'm going to go downstairs and help Bobby do some research on how demon blood affects angels."

"I'm staying with him. I'll make sure he doesn't get worse," Dean said softly.

Sam gave one last sidelong glance at their angel, the angel who had saved them so many times, and prayed to God that they would be able to save him too.

Cas was in pain. Pain was not something Cas was accustomed to feeling, but ever since he fell he seemed to be dealing with it quite a lot. But this pain, this pain was different. It was intense and he felt it throughout his vessel's body. Even his true form felt the pain. It came in waves, and each wave felt worse than the last. Every time his heart would beat, the demon blood coursed through his veins with more force. It was hot and cold at the same time and he was shivering despite his skin being hot to the touch. Half asleep and half awake, Cas could feel the intensity of his nausea growing and he was frustrated that he couldn't just heal himself like he used to.

Cas's eyes fluttered open and he tossed and turned around in all the blankets that were laid on him. In his foggy state, Cas did not recognize that he was safe in Bobby's house, and panic quickly took over as he became more awake. He was trapped. He was in heaven's prison cell. His brothers were torturing him. He tried kicking off the blankets but only managed to get more tangled, more trapped, and more panicked.

Dean, who had fallen into a light sleep, woke up easily to the sound of Cas trying to tear off the blankets. "Hey hey hey, Cas, buddy calm down! You're okay, you're safe. You're in Bobby's house with me and Sam!"

Cas did not seem to hear Dean's reassurances, and he fought against Dean when he tried to hold him down by his wrists. Even in a weakened state, Castiel was still an angel, and still quite powerful. Dean struggled to get control of his friend. "Sam! Bobby!" he yelled out, in need of assistance in restraining the powerful angel.

Sam and Bobby came charging through the door and instantly assessed the situation. Sam grabbed one of Castiel's wrists while Bobby held down his legs.

Castiel was screaming in fear and in agony. "Please! Stop, I'm sorry… I'm so sorry! Please brother, I'll obey! Please!"

It was especially hard for Dean to watch the normally stoic and expressionless Cas express so much fear and pain. He was shocked when he saw tears streaming out of Cas's glassy, blue eyes. His pleas for mercy made Dean even angrier. These hallucinations had to come from somewhere, and he knew that Cas has more than likely been tortured by his brother's before. Nevertheless, Dean continued to whisper reassurances to him, and they finally seemed to be working as Castiel became too exhausted to fight back as hard.

"Dean," Cas whispered as the hallucination wore off and recognition took place.

"Yeah buddy it's me. You're at Bobby's house. You're safe."

"Where is Camael?"

"Who?"

"Camael, my brother. He, he had the knife, and he…"

"Camael isn't here Cas and he can't hurt you okay," Dean spoke softly even as the rage towards Castiel's so-called brothers rose.

"He was going to hurt me, he was going to hurt Ariel."

"Ariel?"

"Yeah my sister, my favorite sister. We always fight side-by-side. They still have her! We have to save her!"

Sam's heart suddenly broke as he recognized the name of the angel, the angel Cas killed just a few days ago. He gave Dean a look and he knew that Dean understood. Cas was hallucinating that Ariel was still alive. The brothers were not sure how to tell him that his sister was dead, and his sister was the one to cause all of this pain in the first place.

"Cas, they don't have your sister."

The tone in Dean's voice seemed to strike some sort of recognition into Castiel. He thought back to three days ago when he had been fighting alongside the Winchester's. He remembered sliding his angel blade deep into Ariel's chest. He remembered watching the light of her grace pulsate and then die as her once beautiful wings charred on the ground. "No…" he whispered as tears once again stung his eyes.

"I'm sorry Castiel," Sam said softly. Sam gave another meaningful glance to Dean and they concluded without saying anything that it was probably best that Sam and Bobby left the room. In other circumstances, they would have let Cas grieve alone, but they all knew that he should be looked over to make sure he doesn't worsen too exponentially. So Dean sat silently by Cas's side as the angel stared silently off into space until his exhaustion finally got the best of him.

Downstairs, Sam and Bobby were flipping tirelessly through the hundreds of old books that Bobby had in his collection.

"Sam I think I found something." Bobby said, unable to contain the hope in his voice. Though he knew that Castiel was thousands of years older than him, Bobby had started to view him as a third adopted son, and he knew the boys viewed him as a brother.

"What is it?" Sam said with just as much hope in his voice.

"It says here that angels can be fatally wounded when demon blood enters their blood stream. Angels are pretty much the definition of purity. When demon blood enters their system, it starts to eat away at that purity."

"Yeah I pretty much assumed all of this. Does it give us a way to cure angels?"

"Hold your damn horses boy, I ain't done reading this thing yet," Bobby replied. "Anyway, since their grace is being eaten alive, the only way to fight the demon blood is to add the grace of a higher ranking angel to the wound."

"Alright this is good. What species of angel ranks higher than Cas?"

"Well, Cas is a seraphim right? So that means the only species that ranks higher than Cas would be the archangels."

"The archangels? How are we supposed to get an archangel to help save Cas? Lucifer and Michael are certainly out of the question. I know Cas and Raphael don't exactly get along. That leaves…"

"Yep."

"No. No Bobby we can't! He's just going to mess with us!"

"Probably, but he is the best option."

"Ugh fine," Sam said defeated. "Just let me tell Dean first. He's going to be pissed about this."

"It's his only chance."

Back upstairs, Dean stared worriedly at his best friend. He watched guiltily as Cas tossed and turned, completely overrun with nightmares. Dean knew that fever dreams were bad enough in humans, he didn't even want to know how bad it was affecting the angel. He figured it would be especially bad since the angel was thousands of years old and has clearly been through quite a lot. Cas would occasionally mutter the names of his siblings or he would start speaking Enochian. Dean wanted so badly to wake him up from his nightmares, but Dean knew that Cas needed to sleep. He touched Cas's forehead again and was disappointed to still feel Cas's burning skin on his palm.

With that, the bedroom door flung open. Sam stood in the doorway and said "Dean, I think we found a cure for Cas. The only problem is we need an archangel to heal him. We need Gabriel."

"You've got to be kidding me."

"Dean, it's our only shot. Without Gabriel's grace, Cas will probably be dead by the end of the week."

"Alright, make the call."

"That's it? I figured you would have fought this more."

"If it's Cas's only chance then so be it. I would rather deal with that dick with wings for an hour than deal with Cas dead for eternity."

"Alright then. I'll make the call."

"Gabriel, I know you aren't our biggest fans, but Dean, Bobby, and I really need your help." Sam looked hesitantly at Bobby, who gave him a nod of reassurance. "We have a problem that only an archangel can fix, and we need your help," Sam continued, "Please Gabriel, we're at Bobby's house in Sioux Falls. This is really important."

After pausing a moment to see if Gabriel would come, Sam continued on, "If you don't come, I'm just going to summon you and you won't have a choice."

"Maybe you should tell him why, you know how much he loves his family," Bobby interjected.

"Yeah I know, but I don't want him to come and immediately smite us. I'd like to just ease him into it."

"I think you'd better tell him," Bobby said.

"Fine," Sam huffed, "Gabriel, it's Cas. He's hurt, he needs you to…"

Sam was interrupted by the sudden sound of wings flapping and papers flying off of the table. Sam turned and witnessed Gabriel standing behind him. He did not look happy.

"So what did you two chuckleheads get my baby bro into this time?" Gabriel said snidely, but Sam could see a hint of distress in the archangel's eyes.

"Dean, Cas, and I were on a hunt, and some angels came and attacked us out of nowhere. I think they were sent to kill Cas. Anyway, we broke into a fight with them and we managed to kill all four of them. However, Ariel cut Castiel's arm and we think her blade was laced with demon blood which is…"

"Poisonous to angels," Gabriel finished for him. "Why should I fix him? Heaven wants him dead anyway. If he survives this they will just keep coming after him."

"You should fix him because you know you would never be able to live with yourself if you were the reason your brother didn't survive." There was not much Sam knew about Gabriel, but he knew this.

Gabriel huffed and tried his best to look annoyed. "Fine. Where is he?"

"He's upstairs."

Gabriel vanished into thin air and Sam heard Dean curse in surprise. Do angels really have this much of a grudge against stairs and doors? Sam thought to himself.

Sam and Bobby climbed up the stairs the old fashioned way and went into Dean's room. Dean was standing in a defensive position, but Gabriel clearly wasn't paying attention. His mask of self-assurance was gone. A look of sadness and fear had taken its place. He touched Castiel's forehead and ran his fingers through Cass's dark brown hair. "Oh Cassie…" He tore off Cas's bandages and had a sharp intake of breath.

"This is really bad. I'm surprised he isn't dead yet."

"Can you fix him?" Dean asked, caution in his tone

"Yes but it's going to take a great deal of energy to repair his grace back to its full health."

"Do it!" Dean snapped.

"Calm down! I'm doing it alright!

Gabriel kneeled down and placed his palm on Castiel's arm. He muttered a few words in Enochian and a blue light escaped from his palm. Sam, Dean, and Bobby watched as the black in Cas's veins subsided and the wound started to heal.

"What's taking so long?" Dean asked guardedly after about five minutes of watching Gabriel in anticipation.

"It's taking longer than expected because the demon blood has almost completely mixed with his blood. I'm separating all of the demon blood out of him. It doesn't help that the demon blood has had so much time to progress without being healed." Gabriel glared at Dean, clearly blaming him for Cas's current state.

They waited for another five minutes, the only sound was Gabriel murmuring the Enochian spell. Finally, Gabriel stopped chanting in Enochian and pulled his hand away from the fully healed wound on Cas's arm. He stood up but staggered a little. The spell had been more draining on him then he initially thought it would be. He shook it off, not wanting to show even the slightest bit of weakness in front of the Winchesters.

"What happened? Is he gonna be alright? Why isn't he moving?" Dean asked frantically.

"Cas is fine, just unconscious. I may have healed the wound but he still needs some time to recover. He'll probably be like this for a little while longer."

"You're sure he'll be okay?"

"If I wasn't sure, I wouldn't just abandon him by vanishing into thin air." And with that Gabriel was gone in an instant.

"Well it looks like he's going to be out for a while boys. I'm gonna do some more research downstairs," Bobby eventually stated.

"I'll come with you Bobby," Sam said in agreement, "Dean?"

"Nah, I'm gonna stay here. Make sure he knows where he is when he wakes up you know."

"Alright, let us know if anything changes."

"Alright."

Castiel was dreaming. He dreamed about Heaven. He dreamed about his brothers and sisters. He dreamed about Sam and Dean. His dreams had become a little more pleasant since Gabriel healed him, but he still had the occasional nightmare. Suddenly a beautiful park in heaven turned into a stormy graveyard. His brothers were fighting one another and when he tried to stop the fighting they all turned to him. Sam and Dean fought by his side but they were quickly overpowered by the angelic army. Cas screamed in agony when he saw angel blades pierce their chests the same way that Ariel had been pierced. After watching Sam and Dean die, Cas fought harder and with a vengeance. Blood lust overpowered him and he began slaying his siblings without much guilt. Then the blood lust wore off. Despair and heartbreak overpowered him and suddenly Ariel appeared in front of him.

"This is what you deserve," Ariel seethed as she sunk the blade into Castiel's chest.

This was enough to shake Castiel out of his nightmare. He sat up too quickly, the world beginning to spin around him. He was gasping for breath and he could feel a thin layer of sweat on his brow.

"Cas?" Dean muttered, half asleep. He cracked open his eyes and saw the angel sitting up in bed, panting like he had just run a marathon. "Oh my god Cas!" Dean shot up and went immediately to his side.

"Dean?"

"Yeah buddy, it's me. How ya feeling? You still look pretty shaky there."

"I feel like I was hit by the angelic equivalent of a bus."

"Yeah Bobby said that was to be expected. He did some research on the spell that Gabriel used to heal you and…"

"Gabriel healed me?" Cas interjected.

"Yeah we had to call him. He was kinda your last chance."

"Where is he?"

"Oh yeah well he vanished about three days ago."

"Sorry man, I know you probably wanted to see him," Dean added after seeing a look of disappointment on Castiel's face.

"So I've been out for three days?"

"Yeah. You had me worried there man. I didn't know if you would ever wake up."

"I'm sorry I was such a burden to you, I'll get out of your way."

"WAIT Cas stop!" Dean said quickly before the angel could take off to God knows where. "Cas don't leave. You aren't a burden on us, really. Please Cas you need to stay here and recover a little more. Besides, I'm the one who should be apologizing, I'm the reason you flew off in the first place, the reason you didn't come to us until you were almost dead. Please, never ever do that to us again, no matter what bullshit I say to you."

Cas stared at Dean inquisitively, making sure that Dean meant it.

"Thank you Dean."

"You don't need to thank me Cas. You're my brother, just as much as Sam is."

"Where is Sam? And Bobby?"

"They're downstairs. I'll go bring them up. I'm sure they want to see you."

"No, I would like to go downstairs, it's quite small in this room."

"Alright man, whatever you want to do."

Dean helped Cas slowly get out of the bed. Cas staggered a little bit, dizziness overtaking him.

"It's alright Cas, take your time," Dean said gently as he pulled Cas's arm over his shoulder. He guided him out into the hallway and they slowly descended the stairs.

"Well look who's among the living now!" Bobby said, unable to hide the joy in his voice.

"Cas!" Sam exclaimed and he ran over to hug the angel that he also considered his brother. Together, Sam and Dean guided Cas to a kitchen chair and set him down.

After a little bit of catching up, Cas paused and looked down at the gray AC/DC shirt he was wearing. "Is this yours?" Cas asked Dean.

"Yeah I thought it might be more comfortable."

"Thank you," Cas said right before he snapped his fingers. Suddenly he was in his suit and familiar tan trench coat.

Dean shook his head and rolled his eyes. "Well I guess near death experiences don't change everybody."