Hey guys! So I've been thinking about this idea in between my Second Generation series. Let me know how you like it! This is separate from that series by the way, so hopefully there's no confusion.

Steve's POV

"Anyone see our suspect?" I asked though comms. Tony and Loki had found a recent spike, possibly indicating an infinity stone. Or at least, that's what Loki had claimed. So, the plan? Follow our guy and grab the stone before it could be in the hands of someone like HYDRA or Extremis. So, we had tracked him down to a small cafe, and decided to wait at individual tables.
"I've got him." Tony called back.
"Don't try anything risky Stark." Loki hissed. "If it is a stone, we are at a severe disadvantage."
"Loki's got a point here Tony." Natasha called. Out of our plan, I formed the first team with Tony and Loki while the second team, led by Natasha, had Thor and Clint. Natasha's team largely waited in the back, ready to assist in the take-down. "Remember, in this case we need to trust those with magic. Loki especially, since he told us about this."
"Uh huh." He grumbled. It was difficult to adjust to Loki on the team, with Tony and Clint refusing to work with him, Natasha and myself acting as a buffer zone and Thor being super enthusiastic to work with him. Bruce? He refused to take an opinion, instead there being a silent sense of respect/fear between the two.
"He's moving." Clint called, watching from his hidden post.
"I've got him." Tony called, this time actually getting onto his feet and walking after him.
"Damn it Stark." Loki grumbled again before getting up as well before walking after Tony.
"Steve, I know its tempting, but do not go after them. Its gonna be a dead give-away if he sees three men following him." Natasha said. I could just picture her shaking her head.
"And two men arguing isn't a give-away?" I sighed before getting up and walking after them.

Loki's POV

I walked after Stark, quickly catching up. By some luck, there was still some distance between us and the man, who clearly held a case to contain this stone. I stepped in front of Stark and said the best way I could,
"At this rate, he'll get away with the stone." Honestly, the man tried my patience. He pushed me away and tried to rush after him.
"He's getting away Loki!" Stark growled. "Who's side are you on?"
"The side that is going to do this properly."
"Enough, you two!" Rogers hissed, breaking us away.
"Thank you Steve." Tony nodded before rushing after the man. I shook my head and said,
"He'll get himself killed Rogers." I warned. But Rogers shook his head and said, "I'll go after him. I should be able to talk some sense into him." He turned and went after Stark. I huffed, muttering,
"This is madness."

There was a period of silence. Not good.
The idiots have gotten themselves killed. I thought. I told them. I told them the capabilities of that stone. "Be careful, I'm coming along."
"Romanoff." I sighed over comms. "I'm afraid-"
"LOKI!" A pained call came over the comms. It was enough to make me nearly pull it away.
"LOKI, YOU-" Another scream. Rogers, Stark. I straightened up and ran towards the direction the two had disappeared.
"Loki-Loki what is happening?" Natasha called.
"Get over here now!" I called. "Steve and Tony are in danger!" I kept running until I heard it again. Not over the comms, but right next to me. I turned and froze at the sight. The suspect, clearly gone for his own safety while the case lie opened, revealing an orange stone. Tony and Steve bathed in an orange glow, screaming and crying in pain as something began to escape their bodies. I was never sure which stone this man had gotten his hands on. Now, now I knew. The soul stone...how? when? Not the time, not the time.

I raced towards the scene, trying to shut the case and save their lives. I couldn't stand them, but I wanted to prove them wrong. I wanted to be the person my brother wanted me to be. I pushed myself forward as the power of the stone started to claim me. The pain, it burned...it drained...I was going to kill us if I collapsed now. I bit my lip tightly as darkness started to corner my vision, I have no doubt that if I looked above myself, I would see something started to escape my body. I fell to my knees, letting out a small gasp of pain.
"No...right there..." I could faintly feel the cold metal of the case and I just used the remaining strength to shut it.
Then the world around me became dark...

Natasha's POV

"Loki, Tony, Steve!" I called as I ran down the street.
"Loki!" Thor called.
"Tony, Steve!" Clint yelled. I shook my head, nothing on comms, the screams became silent and even Loki had shut up.
"You don't think..." Clint asked softly.
"They're not dead." Thor said, shooting daggers at Clint.
"They're not responding." I kept running, leaving the boys behind. I turned the corner and froze.
There in the alley lie Steve, Tony, and Loki, unconscious. The footsteps behind me froze as the boys caught up.
"Oh no.." Steve was curled up in a ball, while Tony was against the wall of another building, appearing as though he previously attempted to get onto his feet but had failed. And Loki? He was lying beside a case, one arm curled over it. Thor instinctively raced towards Loki, bringing his brother into his arms.
"Thor, be careful. I think that's our target." Clint said as he nodded to the case. Clint approached Tony, as I walked to Cap's side.
"Come on Cap. Not like this." I said softly. I began checking for a pulse, softly sighing in relief when I found a small pulse. I went to Thor's side and said, "I'm just making sure he's still here." Thor gave me his approval with a small nod as I moved over, checking for a pulse. Soon enough, I found another pulse, at a moderate strength. I met Thor's gaze and said, "He's alive." I moved over to the case and firmly shut it, using the clips to prevent the case from opening and the stone falling out.
"Tony?" I called.
"He's alive." Clint nodded. "A fairly strong pulse." I nodded and said, "Clint, do you think you can help me lift Steve?"
"Coming." He moved to Steve's side and gently, we got him onto his feet. I kept a firm hold on Steve as Clint collected Tony and Thor held Loki. Luckily, while I had sprinted ahead, Clint had called SHIELD and we were soon brought back to the Helicarrier, allowing Steve, Tony and Loki to be taken to the Medical wing.

Okay! That's it for Chapter 1! I'm kinda excited and curious to see how ya'll will like this one!
Thanks guys!