"This isn't going to hurt him, is it, Tony?" Hank demanded. He sounded pissed, and with reason. Tony had known that Steve's powers had been failing for over a month, but he'd been so wrapped up in Steve's renewed trust in him that he hadn't been able to bring himself to break confidence and tell the team, even when it affected them. He'd been one of about three people to know that the super soldier serum was deteriorating, and now his silence had nearly cost Steve his life. As it was, Steve was in a coma, possibly paralysed, almost certainly dying, his brain activity caught in a series of nightmares.
"I hope to God not." Tony finished snapping the cybernetic helmet in place, and checked the connection to Steve's neural pathways. It was showing green, as far as he could tell, but he waited for Hank to double check it. "If you see any change in his vital signs, make sure to get my attention," he told Hank, who was leaning over Steve's comatose form, then Tony activated the helmet, and stepped inside Steve's mind.
He was Iron Man there, but not in his new armour. He looked down at himself and saw the Mark III that he'd worn when they'd first been Avengers. At first, the world didn't have a form, instead flickering from one intangible image to the next: Steve and Bucky in WWII; Steve fighting Red Skull on a sandy beach; Steve fighting Sons of the Serpent in New York; WWII again with Bucky falling to ash at Skull's touch; Skull imprisoning Steve inside the Cosmic Cube; Steve falling under a sea of attacking Serpents.
Then, a world on fire. It seemed familiar, if from an odd angle. Tony felt the flames tug at his mind. He'd seen it before, but...
But he'd been drunk at the time.
This was the Bowery flophouse Tony had been in when he'd hit absolute rock bottom, and Steve had come to try to moralise him into sobriety. It had caught fire, somehow, and Steve had carried him out, but while he and Rhodey had been busy putting out the fire, Tony had slipped away in search of another drink.
Now he was Iron Man, not Jim Rhodes, and there was no Firebrand, but the tenement was still burning. He didn't want to look inside, to see himself at his worst, but with a certainty one can only experience in a dream, Tony knew that he had to, and knew precisely where to go.
He flew into the flames, shattering a window, and entering a room already half filled with smoke, flames curling in the window and door frames. The other him lay on the flea-infested pallet, as Tony had known he would, apparently dead, his face slack, his bloodshot eyes open and staring.
Steve cradled this other Tony. He was in costume, but the tightness of the armour only showed how gaunt and drawn his body was. He looked skinnier than Tony had seen him outside of historical records, skinnier by far than he looked on the lab bench at Stark Enterprises. He had Tony pulled into has lap, his lolling head resting on his shoulder, with Steve gently keeping it from falling forward with a hand curled around the back of Tony's neck.
"Iron Man," he gasped hoarsely, "you have to help me. Something's wrong with Tony. He won't wake up." His eyes were desperate, and already streaming from the smoke, and Tony knew this was utterly real to him, and telling him otherwise would accomplish nothing.
"He's gone, Cap," he said. "You did everything you could, but he's gone now. It wasn't your fault." And it hadn't been. Neither Steve Rogers nor God Himself could have brought Tony back just then, even if he had been dying.
"I have to save him," Steve insisted. He was clinging to dream-Tony even more fiercely. "I have to make this right."
This clearly wasn't getting Tony anywhere. "I'll carry both of you," he promised, though he shuddered at the thought of touching his past self.
Dream-Tony was already fading in Steve's arms, and Steve himself grew frailer and frailer.
"No," Steve insisted. "No. I have no reason to leave. Tony is dead, and I’m not strong enough to fight."
The smoke roiling across the the ceiling had dropped until Tony had to crouch to see under it. He popped his helmet and pulled it free, coughing against the smoke, which felt real in his lungs, even in this dream world. "Steve," he said. "Steve, I'm right here. Come with me now. You're more than just your strength. You, Steve Rogers, mean more to me than Captain America ever could."
"I..." Steve said, wavering. He looked at Tony in front of him, and the wisps of dream-Tony in his arms. "No, you can't mean that."
Tony dropped so that he knelt at the edge of the cot. "I mean every word. I will tell you in exact and precise detail how much I mean it, but we have to go now." He held out his hand to Steve, and for the longest, most nightmarish moment, He didn't think Steve would take it, that he'd die here trapped in this fire of his own imagining, and take Tony past and present with him.
Then Steve met Tony's eyes, and seemed to see him as he really was. "Iron Man?" he asked. "What are you doing here?"
"I've come for you, Cap. I've come to lead you out of here," Tony told him, and Steve took his hand.
Tony's armour, as rudimentary and presumably imaginary as it was, told him that Steve weighed next to nothing as Tony scooped him up and carried him through the flames to the fire escape. He lay unconscious, his arms trailing and head lolled disturbingly similar to the dead dream-Tony.
"Hang on," Tony muttered, too softly to be heard over the flames. He leaped forward, out of the fire, and into the blackness outside of the tenement. Outside wasn't the dimly lit night of the Bowery, but the dark of deep space, and Tony flew forward into it until the fire faded to a distant spark behind him.
Then Hank shook his shoulder, and pulling him back into his lap, where his arms were empty, and the cybernetic helmet covered his eyes. Tony pulled it off, blinking against the glare of the lab.
"His eyes!" Hank exclaimed, "He just opened them! You did it, Tony!"
But for how long? Awake or not, Steve was failing fast. Tony doubted he could move, and the next heart attack would likely kill him. Fine then, Tony decided. If he could save Steve's mind, he could save his body too. He'd build him a life support system he could wear, like Tony himself had had, all those years ago, when he'd worn the armour Steve had imagined him in.
"You always were a fighter," he told Steve. They'd fight together.