A/N: Set after 9.11. AU Sam and Dean aren't mad at each other for Gadreel. Cain will play a part. First fanfiction.

Dean was sick of it. Sick of all the fights that he and his brother, always seem to fight. Sick of the bickering, and the guilt, that always seemed to follow. He knew his brother would react this way, but he had to keep his promise that he kept his brother in that church. There was no going back now. He thought as he lounged on the chairs within the bunker of the Men of Letters, the place that Dean now called home. He debated to whether to tell them or not, but he knew how their secrets ended up. Cas's reaction was better but not by much. At least the angel was bitching him out like his little over grown brother was. Instead the nerdy angel had pursed his lips in a thin line of worry for his friend.

Dean had taken on the Mark of Cain and while he didn't know the full extent of the effects it may have on him he didn't regret taking it on. Not if it was going to kill that red headed demon bitch queen. He was going to be happy to see her go. Not as happy as Crowley, but close. She was going to pay for what she did to Henry and everyone else. He smirked briefly at the thought, before his mind return to the task at hand. He sighed internally. Time to face Sam's wrath once more.

"-thinking?! You have done some really questionable shit Dean but this! Really?! This takes the cake! Do you even realize what you've done?! Seriously? Do you even know what that mark means or anything? And what the hell are you thinking?! Working with Crowley! How many times has he screwed us over? You're just giving him another chance. My God you're so thick sometimes."

"Sam. Shut up. I know what I was doing. Plus Crowley wants Abaddon died more than anyone else. He knows he's not at the top and that we can't take her down by ourselves. We need as much help as we can get. I know he's going to screw us over again, but when he does, he's going to get my blade through his throat. I did it and I'm doing it because it needs to be done. I mean - hey it can't be worse than what we went through with the trials right?" Dean smiled weakly at his attempt to crack a joke.

Sam winced. "Better not be, or I swear to God I'm going to kill you myself." He mumbled.

Castiel stood up suddenly and strode to Dean. He decided this was the moment to join the conversation.

"Dean. Sam is right. We don't know how this will affect you. We don't know what will happen."

"It'll be fine Cas" Dean waved him off "I know what I'm doing."

"No Dean you don't. You don't know anything about it, do you?" Sam scoffed re-emerging into the argument.

"You know what? It's my decision and it's already made. I realize you guys don't like it, but just go with me on this ok?" Dean's temper flared. He got up and left the room where the two men and the angel were sitting in the men of letters bunker.

Sam blinked and shook his head, shaking his long mane of brown hair. He didn't bother following his brother. He knew he would be back. The oversized man turned his back away from the chair that his brother was occupying just a moment ago and turned to the angel that was taking up residence in their bunker.

"He shouldn't have done that" he muttered more to himself then to the angel.

"He did what he thought needed to be doing." The angel replied. "That's what you Winchester's seem to do. No matter what the effects may be on your health. Taking on this Mark will change your brother. I only worry to what extent. Mentally as well as physically."

"Well geez, Cas, that's not worrisome at all. Thanks." Sam grumbled sarcastically.

Realizing that this was sarcasm Castiel closed his mouth and frowned. He tore his glaze away from the younger Winchester and he looked at the door that his elder friend had gone through.

Dean tore through the doors of the bunker, slammed the doors and began to storm down the hall. He had no idea where he was going. Frankly he didn't care, but he hoped that he would remember the way back to the main rooms. With all that was happening around them, the brothers didn't get a chance to explore the whole bunker. It was huge and yet he found himself in the garage. Walking up to his sleek beloved Impala, Dean decided to do the ultimate thing to calm himself down. Tinker with the engine and give her a tune up. Oil change and a bit of tinkering, that's all. Dean's thoughts had wandered back to the conversation away from the tinkering that as his hands caressed the car's engine. How had his little brother been so forgiving and accepting of what happened with Gadreel and yet slam him for making a decision by himself. He was a grown man. He could think for himself. Hell, he had to think for both of them for a long time, why was it different now?

Because your family. You're not supposed to give up on each other. Ever. You told me that yourself. Why are you changing your mind now?

Dean dropped the wrench that he had been using. He looked around wildly. Who said that? The man's hands automatically reaching for the pistol that he kept in his waistband.

Come on, Dean. Think. Who is able to get into your head?

Like everyone or everything!

Really? I thought my protégé would be better suited then that.

Cain?

There you go! Huh. You're not the brightest crayon are you? Well at least your not the dullest either.

What the hell?! How are you in my head? Get out! Now!

Now, now my young apprentice. You think I would let you go that easily? 'Fraid not. There is much you have to learn, and how do you think you will defeat Abaddon and your other enemies when you do not even know how to control your new abilities?

I-I have abilities?

As this young generation would say- Duh! So guess who is going to be your teacher through all of this. Here's a hint – it's not your angel and he can talk in your head.

So what? You're the Yoda to my Jedi?

In a matter of speaking, yes.

Awesome, my day just seems to be getting better and better. Why are you helping me?

I like to think of it as a way to look for redemption, even though I know that it won't be granted from me, perhaps I can save your soul from hell and spare you the pain. I know you've been through enough, but know that it will get worse before it gets better.

Ugh. Dean rolled his eyes. Of course it will. When is it ever easy?

Shall we begin?

A/N: Bold italicized is Cain's thoughts to Dean. Regular is Dean's thoughts.

Read and Review. This is my first story. I will update as often as I can. Thanks for reading ;)