Spoilers for The Avengers (Avengers Assemble). I loved the friendship between Tony and Bruce in the movie and since the movie ended with them driving off into the sunset together I hope it means that we'll see Dr. Banner in Iron Man 3. I love Tony and Pepper, but I can really see something sparking with Bruce and Pepper.

Also, because I'm clearly not great at finishing on-going stories this is just a one shot. I start my internship in a week so I won't have much time for writing. I'm hoping that maybe this story will spark some others to explore the Bruce/Pepper/Tony triangle.

When Tony had come back to her, after being prepared to give his life to save the city and the Earth, he had not been alone. Pepper had been so absurdly happy to see him alive and well, with that infuriating grin on his face, she had throw herself into his arms and said that she would never let him out of her sight again. Tony just laughed at her, then joked that if she was serious she could always tie him to the bed, but even though his words were flippant he held onto her with the same fury that she clung to him.

That's when she noticed the man still left in the red roadster. He had a serious face, but kind eyes which were kindly looking away from the private moment between Tony and Pepper. For how grave his face was, his hair was a contrasting collection of wild curls, surly made even wilder by a drive with Tony in the convertible. Pepper pulled away from Tony, feeling self-conscious about sharing this private moment with a stranger. Tony didn't allow her to go very far, however, as he kept one arm securely around her waist.

"Hope you don't mind me bringing home a stray," Tony joked, "If you let me keep him I promise to take care of him."

Pepper had heard of The Hulk. She had seen the pictures from the battle in New York where the giant green creature had rescued Tony as he had plunged from the sky. She remembered Tony telling her about him when he had headed out in search of General Grant to find out more about the Avengers Initiative. She knew that he was a science experiment gone wrong on some poor doctor… David… no… that wasn't it. Bruce. Dr. Bruce Banner. In all of that, however, she had never seen Dr. Banner himself. Not until he was sitting in Tony's car.

Tony gave Bruce his penthouse in Stark Tower. The rooms in Stark Tower also came with a private lab downstairs, a smaller version of the one he had in Malibu. "Give Banner anything he wants," Tony had ordered, "Full access to Jarvis, the company R&D, anything the guy wants."

It was strange. Tony didn't trust people easily. Especially not after what had happened with Obadiah Stain. Natasha Romanov had once had a chance to enter his inner circle but that ended the moment he realized she had lied. He may have understood her motives but it didn't mean that he would forgive them. For years it had been the same people who Tony had turned to: Pepper, Rhody, and Happy. Suddenly there was this new guy. It was strange.

"Is it because he saved your life?" Pepper asked him one night.

"Of course not. I didn't bring Captain Caveman home, did I. Didn't even particularly like going to dinner with him. Once the guy found out we were eating goat… like that's so much stranger than a cow?"

"Then why are you doing all of this for Bruce?"

Tony changed the subject by kissing her and that was the last time she mentioned it. After all, it didn't really matter why. Bruce Banner was brilliant. His work was unparalleled. He had already identified an inefficacy in the Arc Reactor powering Stark Tower that they would be able to adjust in future models to make them fully sustainable for 10 years instead of just one.

Pepper was in New York to finish negotiations for a buyout of a pharmaceutical firm when she decided to go visit Bruce Banner and thank him for his work. Jarvis told her that he wasn't in the penthouse and used the GPS to locate him in a rough and tumble neighborhood on the other side of the city. Pepper had waivered before telling Happy to drive her there, but in the end she wanted to see him. It wasn't just to thank him. It wasn't about him at all. It was about Tony. Pepper had always prided herself on knowing what was in Tony's heart, even before he knew he had one. The fact that this stranger had become so important to him so quickly made her wonder if she was losing that power. If she couldn't predict what Tony needed would she really be able to keep him satisfied?

The address was a free clinic in a crumbling brick building. Pepper knew she looked ridiculous in her suit and $500 heels as she stepped into the waiting room so packed with people that some just sat on the floor, coughing or rocking their children.

"Hello," she said to the haggard woman at the desk, "Is Dr. Bruce Banner here."

She didn't even look up, just handed her a clipboard. "Fill this out and get in line."

"I don't need an appointment. Is Dr. Banner here or not?"

"I'm here," he said from behind her. He held a small child who was grinning at him. He handed the child to an older woman and started speaking rapidly in a language she didn't understand, odd since she was fluent in five languages. Bruce ran his hand gently against the child's cheek and then handed her to the woman. He called to the woman behind the desk to start the next patient prep and that he'd be back in a few minutes. With a slight tilt of his head he gestured towards the door.

"I'm sorry to be interrupting your work," Pepper began, the words spilling out of her. She didn't know why she was here talking to this near stranger. "I should just leave and let you get back to everything."

"Ms. Potts, you did come here to see me, correct? I assume you weren't just driving through the neighborhood." He crooked his arm towards her, like a character in an old movie offering to escort a woman at a ball. "Why don't we take a walk?"

Pepper looked around. "Are you sure that's safe?"

"Are you afraid of the neighborhood, or me? Because the later can more than apply handle the former. And unless you are concerned that this will be a particularly stimulating conversation then…"

She placed her hand on his arm. "Are all science nerds as sarcastic as you and Tony?"

"No, just those of us who spend our free time saving the world."

They were silent as they went past the first block. Occasionally someone would wave to them, or more precisely to Bruce. Did they know who he was? That they weren't just being treated by a kind hearted doctor, but by the world's leading expert in cellular biology and gamma radiation.

"It's great that you are doing so much charity work. Tony is a big philanthropist."

"Yes, I've read about the many organizations he names after himself."

She ignored the condescending note in his voice. "If you want we can make a donation to the clinic."

Bruce chuckled to himself. "That won't be necessary. What would they do with the money anyway?"

"Oh, I don't know. Buy chairs. Or maybe move out of that dump into someplace nicer. Hire some staffers who don't look like they are re-animated zombie corpses."

Bruce's jaw clenched for a moment and she suddenly felt a cold wave of fear. "Don't get upset. Not now, not here."

His big brown eyes looked at her sadly, like a puppy dog. "Seriously? If some ill-informed privileged rhetoric was enough to turn me then I would have never lasted five minutes with Stark."

She wanted to trust him, but the adrenaline was coursing through her. All she could think about was the tape of what he had done in New York, and that was when he was under control. If he was really angry how could anyone stop him?

Bruce could feel her nervousness and he took her small hand in his and pressed it against his chest, right above his heart. "Count the beats for the next ten seconds. I'll tell you when time is up." Pepper froze for a moment, feeling the strong thump of his heart under her hand. She counted. One, Two, Three, Four… he was shorter than her. Even in bare feet she'd have a few inches on him, but in her heels she towered over him. Even so, there was something overpowering about his presence. It was the opposite of Tony's arrogant and bold charisma that tackled you the moment he walked into the room. Bruce gave off something every bit as powerful, but unyieldingly still. Tony's arms were passion and fire. Bruce's were protection and safety.

"Stop," Bruce said, pulling away from her. "Now, if it is up above 200 beats per minute then we start getting into dangerous territory. But just getting into a little verbal sparring match, shouldn't be much more than 75 or 80." Pepper started walking again and he took a moment to catch up.

"Money is great," Bruce said, "But the clinic already looks like Mount Sinai compared to what passes for medical care in large parts of the world. So, it looks a little run down. The whole neighborhood looks like that. We could move it to a better neighborhood, but then it isn't serving the people who need it. And the staff might be less than perfect, but they're doing it because they want to. Stark could hire the best doctors in the world and pay them enough so that they'll trek down to this part of town and work with these people, but they'd be doing it for the money. Not because they actually cared. And I'd rather have the guy who graduated at the bottom of his med school who wants to be here than the top docs in the world who are doing it for the money. The only thing we really could use help with is getting the more expensive drugs into the hands of the people who can't afford them and…"

He abruptly stopped talking, realizing he'd said too much. It was too late. Pepper had already figured it out. "That's why Stark Industries is buying a pharmaceutical company. For you."

"It's not for me, it's for them. And I'm sure Stark will manage to end up making it into some huge PR thing that will get him even more money in the end."

This was it. The moment she had been dreading. The time she had to ask what she had come here to ask. "Why is Tony doing all of this for you? It isn't because you saved his life. It isn't because some Stark technology was responsible for the accident. Tony doesn't just trust people. He doesn't just bring them into his life. He's had the same group of friends for over a decade, and most of them are robots or machines. Then he spends a weekend with you and now you guys are bffs forever."

Bruce took of his thin-framed glasses and rubbed his eyes. He put them back on and looked up at her, a strange intensity, his brown eyes seeming almost hazel in the light. Pepper was mesmerized, unable to move another step.

"Do you know John Bradford," he said, and then without waiting for her reply continued, "He was a martyr for his faith. Locked in the Tower of London by Mary Tudor he was looking out of his window when he saw an execution. He said, 'There but for the grace of God goes John Bradford.' God wasn't all that graceful because he ended up in the noose not long after. Although, now that I think about it, it might have been a burning and not a noose."

He shook his head. "I guess that isn't important. My point is that Stark and I are opposite sides of the same coin. There but for the grace of God and he could be me, or I him. We both had our lives upended by our own work. The only difference is that after he almost got blown to bits by his own weaponry his life became better. He found a purpose, he let himself experience love, and he is a better man now because of it."

"And what happened to you?" Pepper asked.

Bruce hesitated. It didn't matter. He told himself that she didn't need to know, but there was something about her. She was so self-reliant, and fearless, and so much like Betsy had been at one time.

"I lost everything. My life's work had turned me into a monster. I nearly killed the woman I loved, and even when we reunited it wasn't the same. She loved the man I was before, and she couldn't understand that I had changed. I had to turn my back on the world and go into hiding. I had to say goodbye to the Bruce Banner who had once existed and become someone else."

He hadn't spoken about this ever, not even to Tony Stark on that long drive back after the battle where they were telling each other so much about themselves. This was new, and with it came a sudden revelation that he couldn't keep from saying aloud.

"Even though both of our lives changed permanently, neither of us regrets it. We wouldn't go back to the men we were, not now that we've seen who we can be."

Pepper squeezed his arm. "Thank you."

"For what."

"For trusting me enough to tell me that. For helping me understand. I loved Tony for years, long before he loved me back. I loved the man who he could have been, and that's the man he has become."

"He's a lucky man." Brue thought about Betsy, his chest suddenly feeling hollow. "Betsy loved me as I was. She didn't realize that it was a façade. The entire time we'd been waiting to come out and the accident was just the catalyst, not the cause."

"You'll find someone. I'm sure you will. You're a good man."

He gave her a tight smile. "I might be a good man, but that's why I'll be alone. A woman deserves a life above 200 beats per minute."

Pepper leaned over and gave him a kiss on the cheek. Her long red hair brushed is face and he had to take a breath to control his emotions. "Tony and I will be in town next week for an investors meeting. Can we take you out to dinner?"

"I'd like that."

Bruce waved to her car as it drove off and then walked back into the clinic. He felt terrible lying to her, but justified it to himself by pointing out it wasn't really a lie. He and Stark did share that strange connection, but it wasn't what bound them to each other. He couldn't tell her the real reason. How could he ever explain that he was there to kill her lover?

They had made the decision the night after the big battle. The Tesseract would be going back to Asgard soon. Bruce and Tony were in the lab getting some last minute readings from the device. As they waited for the computer to finish an analysis Bruce looked up to see Tony staring at him.

"What? Do I have that weird sauce on my face from dinner?"

"No, I was just thinking how amazing it is that while we all look like we were nearly killed…"

"Because you were all nearly killed."

Tony ignored him. "We all look like we were nearly killed but you are fine. When you change, you don't retain any injuries, do you?"

"None yet."

"You're indestructible," Tony said, amazed.

"I know. I took the fall that S.H.I.E.L.D. thought would kill me and I woke up fine. The only good thing is that the other guy isn't all that bright. He could probably be trapped and knocked out long enough to allow me to return."

"We developed this sonic weapon," Tony explained, "It paralyzes any living thing for about 15 minutes. Would that be long enough?"

Bruce was suddenly very interested in this conversation. "It could be. We'd have to find a way to test it but… you could stop me if necessary."

Tony clapped his hands. "I could. But I need you to promise to do something first."

"What?"

"Kill me."

Bruce shook his head. "What?"

"Not now," Tony explained, "Not ever, hopefully. But the God of wacky hats tried to take control of me. If he had succeeded I would have been unstoppable."

"We did just save the world, I'm pretty sure the Avengers could handle you."

Tony slammed his hand against a counter. "I'm being serious. Look, one of the best pilots the Air Force has ever seen took me on in one of these suits and the only thing that got damaged was my house. I went toe-to-toe against a GOD and it ended up in a draw. Sure, you all working together might be able to take me out, but you wouldn't get the chance. Because I'm not just strong, I'm smart. Smart enough that if I was ever going over to the dark side I'd start taking out The Avengers one at a time."

"I don't want to talk about this."

"Too bad," Tony yelled, "Because we need to. You know what it is like to worry that you might one day hurt the people you care about. I need a fail-safe. Something that I can count on to be there and protect everyone from what I could become. You need that too. And we can be that for each other."

That night they shook hands and made it official. Bruce Banner and Tony Stark might be friends, but the core of the friendship was a promise of mutually assured destruction. Hopefully the day would never come when Iron Man faced off with The Hulk, because only one of them would return at the end.