Title: Doors Open on Both Sides

Things to know: This is my fan fiction story go I am not picturing Gary Oldman but Ben Barnes but with grey/blue eyes, some websites have him playing a younger Sirius Black so you've probably seen him. If not, he plays Caspian in Chronicles of Narnia. It will have slash later on and it will be Clint/Harry. (A friend of mine really likes that ship) Any other ships will happen as I feel like it.

Elements of both side will be used. I am also familiar with Harry Potter's Death[the entity not his actual death.] than the Avengers. I know she is female, but the point of a crossover is to bring two worlds together by using some parts of each. Avenger's world, if Death is needed, it'll be HP's Death.

I am making this up as I go along, there is no plan, no definite idea, just going along with the punches and seeing how they roll.

Also not BETA'd and with my schedule and crap, I probably won't get one either. It's for fun not profit so it doesn't matter either way.

Sirius took a sip of his tea as he sat in his flat reading the morning post. He heard the buzzing of his mobile somewhere in the flat but he chose to ignore it. There were very little people who would call him and they knew better than to call him these days. He was always in a bad moon these days...it was the anniversary of his 'death'.

Just as he was about to get up for another cup of tea there was a knock on the door. His ward protection told him who it was and he sighed. 'So much for a peaceful few days.' he thought.

When he opened the door he leaned on the threshold, arms folded over his chest, and his signature smirk in place, "Well Coulson...I would expect this from Barton but usually you have more manners, mate."

Coulson gave him that ever infamous smile of his as he gestured inside, "Mind if I come in Mr. Black?"

Sirius made a face, "Yeah kinda...I thought you knew I was taking some personal days. Not to mention...I don't work for S.H.I.E.L.D remember?"

"Yes, kind of hard to forget you turning Fury into a ferret when he kept insisting. Barton still has the habit of calling him furry." Coulson deadpanned which made Sirius smirk at the thought.

"Then why come and bother me now?" Sirius asked as he gave in with a sigh and let the other man in. The wards were really more to notify him of nearing presences rather than hide his location and keep others out. Soon after arriving in this world he learned that he needed S.H.I.E.L.D in some ways. He hated it but he screwed around with them when he felt over crowded.

The agent nodded in thanks and entered the apartment. "I so apologize for interrupting your morning, Mr. Black. But we want you to look over something. You may not work for us but you do consult from time to time."

"Only when magic is involved," he added as an after thought as he accepted the file Coulson handed him.

"Or the Tesseract...it's how you yourself came to this world," Coulson corrected.

"Even then, I'm not a scientist...I can't tell you anything since I don't understand it." Sirius replied.

"Well...Dr. Selvig has added some new notes. We think it best you read them over." Coulson said.

"Giving me this to read is like giving me something in Ancient Greek, you do realize it right?" Sirius asked with a raised eyebrow.

Coulson grinned tightly before serving himself some tea, "We know that a lot of people think that magic and science are two different worlds. But there is a chance there can be a connections. Maybe one we can't see right now."

"Or alchemy. That's what some muggles know it as." Sirius deadpanned as he opened the file and read through it. For the most part it seemed like the Cube has been quiet since his episode. A few energy signature spikes but overall quiet. "So, out with it...why are you here? And please...feel free to use some creativity."

"We think you and Dr. Selvig can do more with this if you meet up and help him understand." When Coulson saw that Sirius was about to reply he added, "Magic is an energy source isn't it? Well so is the Cube. Just come and have a look. It's all we're asking."

"On today of all days?" he asked.

"The sooner the better," Coulson answered.

"What's going on?" he asked.

"...we've been under a lot of pressure and we'd like to have more answers about the Cube." Coulson said with that smile of his again. Sirius was really beginning to hate that smile.

With a sigh he stood and said, "Let me get a few things. I assume you can fly me over?"

He didn't wait for a reply but he did smirk on his way to his room. Remember the time he Apparated into S.H.I.E.L.D and the electricity went on the fritz. His magic was not compatible with their technology. He's also Apparated with Coulson, Barton, and Romanoff and none of them like his style of travel no matter how convenient it was.

In his room he pulled an already packed duffel from the closet and laid it on the bed. There wasn't much...there never was. He still had his memories of being on the run and how he had to go with even less then. He looked in the mirror and stared once more amazed at what happened to him. Going through the veil was at first like falling into water. Coming out of the veil though was like crashing through a glass window but worse. It was like his body was pulled through broken shards of glass and he felt the void's presence and powers all throughout his body, veins, and mind. When he first got a chance to look at his reflection he was amazed to not see that strained, tired, gaunt face that had developed over his years in Azkaban but rather...what he would imagine his face would look like had that nightmare never happened.

His tattoos were still there, but the scars weren't. He could actually sleep, like if there was a block on his mind while he slept. And his hair...his hair was amazing!

He ran his hand through his said amazing hair, he always liked it long and it was growing again, having cut it about a year or so ago.

He zipped up the duffel and went to his night stand. He had a small pouch that he took everywhere with him. It held some glass of his communication mirror he had given Harry so they could stay in touch. He looks at it a lot when he has free time, hoping that there may be a connection one day. Sadly, he always just stares back at his own eyes.

"Ready to go?" he asked as he came back out of his room.

Coulson nodded and lead him down stairs and into a modern black vehicle provided by S.H.I.E.L.D. Sirius really rather preferred his bike but got in without question.

"She asked about you again, you know." Coulson mentioned as they drove.

"She probably asked if I got killed by trying to use a toaster or some other muggle piece of tech." He scoffed as he thought about the redhead who would be 'asking about him.'

"You know her quite well. Not many do." Coulson remarked.

Sirius couldn't help but smirk, "And I bet it pisses her off she doesn't know much about me, eh?"

Coulson chuckled, "She wouldn't be the only one."

"And that's how I like it." he said

He remembered laughing...he could feel victory. Then he saw his cousin and the flash and then coldness. It felt like he was floating in water before the pain started and he crashed through. He gasped for air, something he thought he'd never do again and opened his eyes as he heard sirens, heavy footsteps, and yelling.

When he opened his eyes he was surrounded by people and guns. A woman with black short hair in a pony tail demanded, "Who are you?"

His mind was still still foggy with pain and shock that he answered anyway, "Sirius."

Someone, a male voice asked in a hush tone but his dog like senses heard it anyway, "Seriously?"

"Common misconception but my middle name actually isn't Lee."he groaned out as he tried to move. Instantly he heard their guns cocking so he laid back down with an eye roll. "Fine whatever...too tired to move anyway."

The woman who asked him who he was then asked, "Where did you come from?"

"Unfortunately, my mum." Sirius replied as he closed his eyes.

The guy who asked 'seriously' laughed and Sirius smirked.

"I'll ask you once more. Where did you come from?"

"Look doll, when you figure it out, feel free to lemme know. Until then, am I allowed to get up or can I just fall asleep. Dunno what the bloody hell I just went through but I'm exhausted."

There was a silence before he was lifted up and dragged away by a blonde man he'd later know as Clint Barton. Sirius called back, "Is it because I'm a Brit and you're a Yank?" all he got was a snicker from the guys dragging him off.

He was placed in an interrogation room to wait. After just a bit of half an hour a red head appears with a sway of her hips and a grin on her face. She acted flustered and Sirius laughed out right, causing her eyes to widened. When he calmed down he smirked and said, "Babe, I've played this game before, hell I practically lived it every day my whole life...you want anything out of me...bring it up a notch."

She never got much out of him, and it bugged her. Sirius Black was the one puzzle Natasha Romanoff could never completely solve and it amused Sirius greatly.

"So...you wanna tell me what's going on?" Sirius tried again.

"Everything is just fine, Mr. Black." Coulson replied.

"Right...but when the shite hits the fan, I'll be the first to say 'I told you so'." Sirius said.

"That doesn't make sense." Coulson stated.

Sirius rolled his eyes, "I'm a wizard, I don't have to make sense."

Coulson shook his head as they parked near the hanger and they made the way to the plane. Bag on board, Sirius took a seat and watched as the S.H.I.E.L.D jet took off and towards HQ. He idly wondered what the hell he's gotten himself into. Knowing himself as well as S.H.I.E.L.D it wasn't anything good.

Read warnings in the beginning.

TBC