It is the simplest equation he's ever conquered in his life.

And let's not lie, solving equations is a conquest for him. Each problem is a battle that tests his mettle – some more than others – driving him to work and create the way that war challenges a warrior. It tests his limits, which, of course, he has none, because every time they're tested he pushes them further and further. If they exist, they're made of elastic, and tend to bend whenever he puts his mind to it.

Simple equation. Right. Back to that. He's sitting in his office at some early hour of tomorrow, because anyone who stays up all night knows tomorrow never begins until your head hits the pillow… if it hits the pillow. There's a plate of food and an empty coffee cup by his elbow; the food is freezing cold and the fork was never moved. Tony is staring the answer to the equation down, and it is staring right back like the proverbial abyss.

It has been… what? Three, four months? Since the Avengers Initiative first succeeded with flying colors and everything has changed. They saved Manhattan – well, he saved Manhattan, but he'll allow that the others had a hand in saving his life. (Hulk, mostly, and oh did he want to say I told you so but he figured pissing Cap off in front of 'the other guy' might not be a good idea). But back on point, everything's changed, and it's been bugging him ever since he first figured out everything had changed as to why the change occurred, because there can never be a change without a catalyst. He should know that better than anyone.

Tony leans back in his desk chair, propping his feet up on the table next to cold meat loaf and potatoes, and he stares at the translucent screen which bares both the answer to his question and the irritation currently keeping him awake. The answer's simple, but he can't start at the answer, no, he has to reevaluate the equation. Whatever people say about him and his 'talk now, think later' policy, when it comes to his work he thinks everything through three times three different ways and then sleeps on it for maybe twenty minutes before realizing he'd been right all along, of course, and plowing ahead.

The equation is, well, it's theoretical, and Tony doesn't usually deal with the theoretical, he likes solid math he can mold and touch. But this time he's working with imaginary things, with scenarios in his head.

There's always been an ache in his chest where the Arc Reactor currently sits, even before Afghanistan. It was what he now recognizes as emptiness, and even though the reactor saved his life it certainly didn't fill the hole underneath, where his heart should be. That callow darkness was both his shield and his worst nightmare, and it embodied him; his heartlessness, his lack of emotional attachment to anyone, least of all himself, which was so painful to endure that it often surged out of control and lashed out at others. Of course the blame is on him, he's a grown man who can control himself – or should – and it was his fault. He just realizes how the math works when he factors in his own lack of responsibility with that previous empty state, in addition to the stress and pain of daily life. Those things together resulted in the mad mess that was Tony Stark, only a few years ago.

Then Afghanistan happened. He used to think of his life as two stages, before and after 'The Cave', but since the change he's started thinking in three's. That's beside the point; he's jumping ahead, one step at a time, Stark. Then Afghanistan happened and the imaginary wall built between him and reality shattered. He had a long heart to heart with his own dickish-ness and realized there had to be some change. Back then, he did the math and figured the odds were low of that happening, ever. But low odds had never stopped him before so he tried, damn it he tried, if anyone can ever say anything of him, it's that he tried. Those two words ought to be his epitaph.

So there was Afghanistan and Obie and Pepper and 'I am Iron Man' and that whole year of madness that was his first year with the suit. Obie. For being a genius, he was an ass at guessing character. It should have been obvious, in retrospect, it was, but he'd wanted to believe so much. Obie was one of his only close… something, one of his people, and to cut him out of his life was to cut Tony's natural interactions with relatively-friendly individuals down by a third. In the end, Obie had cut him down. That still hurt, and he liked not thinking about it. He used the couch he'd been sitting on when Obie stunned him as target practice.

Tony dubbed that year 'the year of too many fucking surprises', because that was when Fury and Vanko and Romanoff and his dad all appeared – or reappeared, as it were – in his life, and he was faced with dying, and then suddenly faced with living again. Not just living, but living with Pepper, and Rhodey didn't hate him (though he still didn't give back the suit), and all in all it was a good year despite the clusterfuck it started as.

Of course, if his life has taught him anything, it's that all good things come to an end, and they come to an end because of Tony Stark. Every equation which adds Tony Stark to anything comes back negative. He and Pepper lasted for a whole year – a year! – before the inevitable end. It was going to happen eventually. Her work as CEO, his work as billionaire genius playboy philanthropist kept them apart, as did physical distance, and emotional. Pepper is perfect in every way, and she deserves so much better than Tony Stark.

Tony Stark + anything else = disaster. Which is why he doesn't really push Fury when the man tells him Iron man is wanted for the Avengers, but Tony Stark is not recommended. He totally understands – if he could just take the suit and leave Tony Stark behind for a while, for forever, it'd be great. But he wasn't lying when he said the suit and he were one, and as much as he'd love to just not be himself, he can't be Iron Man if he's not himself as well.

Somehow it went from not being on the team, to being on the team. It is baffling to Tony despite how much the equation makes sense (end of the world + need for armored hero = Tony can play with the big boys, now.) He's still surprised Fury made the call, though certainly he's made harder calls. But none of that's the point – the point, is that the change started then. All because some upstart god got it in his horned head to strike a deal with aliens.

There was the Captain, who was at first glance underwhelming but in retrospect, every bit the hero Tony's father made him out to be. Sure, initially he appeared bland, vague, dull, too concerned with listening to authority, a little less heroic badass and a little more awkward dork, but none of those flaws could compare with Tony's own, so he's inclined to forgive the man. Plus – unlike Tony – Steve's strengths more than make up for any social awkwardness he has, what with his selfless nature, his upstanding moral fortitude, and his uncanny ability to see right through Tony to the ugly truth few ever admitted was there. More than seeing it, Steve had the guts to tell Tony face to face just how little he mattered. Not that that was news to him, or anything.

Then there was Bruce Banner, Mr. Anger Issues himself, whom Tony was surprised to find he genuinely liked. Ten minutes of trying to provoke him for the hell of it turned into many hours of cheerfully working together. The last time he'd ever been able to talk to anyone on that level that closely, about his work had been Yinsen... Though he didn't realize it when he offered, Tony really liked the idea of having Bruce around Stark Tower, because he was the kind of guy he could see himself getting on with pretty well. Intelligent, able to put up with his crap surprisingly easy, and anything but boring. He was sort of disappointed when Bruce never showed up those first few weeks. Which was hinting towards the answer to the equation, but not there yet.

There was Thor who, despite the violent introduction, was quite easily one of Tony's favorites. He liked Bruce for his brain, but he liked Thor for his vibrant persona. The man was hilarious. If ever Tony was to imagine a God in human form, Thor is the opposite of everything his brain could come up with. The guy's just… he's hardly the all-powerful, omnipotent deus ex machina Tony would imagine if he ever began imagining that Gods were real in any capacity. Which is half the reason he's so funny. The other half has to do with his complete obliviousness and naiveté which is so unfitting for a god, and yet, so endearing too.

And Natasha. Ah, Natasha. Tony has known her longest and yet, knows the least about her out of all of them. He finds he has a healthy mix of awe-like respect and healthy fear for her; though if he told anyone that they might laugh. What man fears Black Widow and makes light of the Hulk? A smart man of course, Tony would reply, because anyone with half a brain cell can tell that Hulk is predictable and manageable with the right mindset, where Natasha is furious when unleashed and impossible to fully predict. He's not sure they'll ever be on friendly speaking terms but he admires her tenacious cunning.

Then there's Clint, who Tony knew even less than he knew the others. But for those short hours, Legolas seemed like a nice guy. They both shared a love of snarky humor, though Clint favored a drier, more sharply sarcastic tone where Tony liked to lay it on thick. As far as he could tell, there was nothing about the guy that could keep them from working well together. Well, at least, not on Clint's end…

So, this strange and awkward team had come together to fight a god and his alien army and had somehow, against all odds, won. Then, just as suddenly as they'd come together, they'd fallen apart again in not a week. Ready to be called upon at a moment's notice, but no longer close by. Thor had returned home with Loki, Natasha and Clint disappeared back into the misty maze of intrigue that was S.H.I.E.L.D., Steve was… somewhere, and Bruce ran off to hide on another continent.

And Tony is here, sitting next to cold potatoes, staring at his computer screen with narrowed, tired eyes. The only lights in the room are coming from the screen itself, and from the flashlight permanently imbedded in his chest. He is reviewing the data and coming to the same conclusion again, and he does not like the conclusion.

On the screen is a website showing the day's biggest news topic. It is innocuous, bland even. He's not even really processing what the article's about; he's just noticing what it's not about. There's no global catastrophe, no alien invasion, no madman running around proclaiming himself god. The world is peaceful today.

And it is pissing him off.

Which leads to him looking over the data again, examining his own conclusions and his – eck – emotions, and realizing there is only one thing that this could all mean. The events of the past months, hell, the past few years, in addition to how everything played out and how he feels about this, can only add up to equal one thing.

Tony Stark is lonely.

And he is really, truly, sincerely wishing the world would get itself into some sort of horrible trouble, the kind of trouble which requires Avenging, because he would much rather have a legitimate, much less pathetic reason for reuniting with the others than just missing them.

He does miss them, and it bothers him that he misses them, because Tony Stark never misses anyone. He doesn't miss Rhodey because he knows his friend will always come back after his tour of duty, he doesn't miss Pepper because she's always one phone call away. Stark doesn't miss people. Missing people is for misanthropic teenage sob stories who like to pretend that wishing for something really hard will make it happen. Tony is pointedly ignoring that he is currently making wishes himself.

The problem is, he doesn't know that he'll ever see the other Avengers again. What if Thor can't come back from Asgard, or just chooses not to? What if Bruce vanishes, swallowed up by the chaos of the world, moving from one trouble spot to the next? What if Natasha and Clint remain entangled in S.H.I.E.L.D.'s web forever? And Steve… what if Steve just doesn't enter into the new world?

Realistically, Tony realizes the world will be in trouble again, soon, but for once his mind is being overpowered by the strangling, suffocating feeling of doubt. Tony Stark doesn't doubt. The word isn't even in his vocabulary, except, it is now, because he's doubtful that he'll ever see those people again.

He tries to convince himself that this is all ridiculous and he could be working on a thousand projects that don't include staring at a computer screen like a forlorn lover. He even imagines he would be better off sleeping, which is something Tony Stark rarely admits. But he can't shake this off.

For years, emptiness filled him with cold and ice; after Afghanistan, he began to chip away at that feeling, working hard to be a different person. But now, after the change, he feels that emptiness again. Not because he's regressing to the person he was – but because, for the first time in many years, he is looking at his life and realizing just how very empty it is. He is realizing this in the way only a man who had that emptiness filled to the brim, and then suddenly emptied again, can.

Thud. Thud. Thud. BAM.

Steve hardly notices he's shattered another punching bag. His eyes catch the sand spilling across the floor, but he doesn't really think about it. His mind is a thousand miles away. He's in another time; though, for once, it's not seventy years ago. No, the Captain is stuck on one forty-eight hour period, four months ago, during which he made many assumptions and just as quickly had those assumptions shattered. Like the bag, cracked wide open, it's filling spilled across the floor, his presumptions had been torn apart.

Hardly breaking a sweat, Steve bends over to pick up another bag then sets it on the hook. He falls back into the motions, each punch bringing back a moment, a photograph of a memory, each motion pulling him back into thought.

It is only after his teammates left that Steve realized he owed quite a few of them an apology.

Thud. Banner wonders what Fury's thinking, keeping him in a submarine. Thud. Banner is holding the staff, staring them all down, angry but lacking green eyes. Thud. Banner is driving up on a dingy little motorcycle, taking all but one of them by surprise.

Steve had thought he'd accepted Banner when they first met. He'd felt guilty in a way, since the formula which made him is the same one which unmade Dr. Banner and tore him in two. What he didn't realize was that, the whole time he was 'accepting' Banner, he was pushing the Hulk away, and to try and tear the two apart is futile. They are one, even if they aren't the same, and it wasn't until that final battle that Steve realized that, and realized what he'd inadvertently been doing in his treatment of Banner.

Thud. Iron man is touching down in Germany, his arsenal aimed at Loki. Thud. Stark is tempting fate with Dr. Banner in the lab. Thud. Stark's voice says 'Keep me posted' through the com, still believing Banner will come. THUD – crash!

Without pause, Steve replaces the bag and gets back to work. Tony Stark. While he owes the man an apology, he cannot help but be thoroughly aggravated by him as well. It's not all Tony's fault, though undoubtedly, a lot of it is. It's just that, Tony is like Howard in so many ways and unlike him in so many others; and it seems unfair to haunt him with a ghost from his past that also happens to have the tact and delicacy of a rhino. Steve isn't especially fond of Tony, but he knows he was unfair to him when they first met.

He realized that he's not as good a judge of character as he'd thought as soon as Tony told them about the missile and declared his intent on what to do with it. He realized, in that moment, that a man he'd thought was the most selfish, self-centered asshole on the planet was about to give his life to save Manhattan and the lives of everyone there – their lives. He realized that Howard Stark's son was about to die saving his life.

He knows now that he was unfair to Stark, and as deserving as he is of criticism in many areas, he isn't the man Steve thought he was. His initial disappointment in the man Howard's son had become is alleviated, even if Tony does make an ass of himself whenever possible. Steve realizes Tony's not as bad as he'd like people to think he is.

Thud. Thor is quick to say Loki was adopted. Thud. Natasha is giving him a nod in greeting and pointedly ignoring him in a way that says she's not impressed by his very presence the way many are. He likes that. Thud. Clint is preparing for battle, telling Thor to get in line behind him for vengeance against Loki.

He realizes now that he was somewhat unfair to all of them, though mostly to Bruce and Tony. He'd dismissed Thor immediately after hearing he was a 'God', because how could that be true? Natasha and Clint were both good soldiers, but he'd distanced himself from them just like the rest. He'd taken to doing that after waking up; it was hard to take everything in, and being around others who'd lived all these years made it that much harder.

He thinks he wouldn't mind seeing them again, especially since he owes at least half of them an apology – won't that be fun, he thinks, imagining Stark – and he honestly didn't mind working with them. They made a good team and they got the job done. Though next time they go out to eat after a mission, he's not letting Tony pick the place.

It is two days later, and Tony is tinkering. He realizes he's not alone, and the fact that he didn't hear a single thing when the person entered the room tells him exactly who it is.

"You know, one of these days I'm going to install a security system that works," Tony mumbles. "Maybe include some lasers, heat rays, a device that senses the amount of eyeballs on the person entering the room." He slides out from under the car, looking up to the one-eyed man leaning on his vintage vehicle. "It'd hardly stop you, but it might give you a headache and I am just petty enough to take pleasure in that."

"You give me enough headaches, Stark," Fury replies with no venom, just as unreadable as ever. He doesn't say anything else, which strikes Tony as odd, since if Fury is anything, he is frank and to-the-point.

"So…" Tempted to simple slide back under the car, Tony remains where he is for another minute. "Is this just a friendly visit, you missed me, wanted to have a chat, because if that's so then who are you and what did you do with –"

Then Fury draws an envelope out of his jacket and shoves it at Tony. The man is taken off guard, at first, taking the envelope as if it might be another disaster about to assault the world. But then he opens it, and reads it and all the snarky humor fades from his face. Fury watches with something almost like sympathy but he never says a word. Tony mumbles something like an affirmative and the man leaves, allowing Tony to sulk in his misery with no remorse.

Phil Coulson's funeral happens on a cloudy day bereft of sunshine. It is a small gathering; he had no family, no friends outside the organization. The only civilian present at the event is the Cellist he'd been dating. Everyone else is S.H.I.E.L.D., or an Avenger.

This is not the way Tony imagined he'd meet them again, but that's not on his mind right now. His mind is stuck on rewind, revisiting all those innocuous moments, those short conversations he'd had with Coulson. They'd never been close, never gotten the chance, and Tony blames Loki for that. He might've understood the guy a little, even realized they had some uncanny similarities, but Loki killed Coulson and that is that.

There's more Avengers there than he'd have thought; Thor is there, dressed in his usual garb, which would have been insulting from anyone else. The Cap is there, Tony realizes begrudgingly, and he purposefully puts some space between himself and the hero. If that space means Tony is standing next to Bruce, that's just a happy accident. The man looks healthier than he has in a while, and Tony nudges the man a little. It's not so much playful as it is comforting. At least, that's what he hopes it conveys, because anything more overt is… not his style.

A priest begins to speak and Tony mostly drowns him out. He thinks of patterns and mathematics, of inequalities. He thinks of how the world has lost Coulson, and yet he is still here… he tries not to think like that anymore, but years of practice make it inevitable.

He's not sure how long he's lost in thought, though no one is speaking when he looks up next. The priest has departed, the coffin has been lowered. Tony sees Steve step forward, his eyes staring at his hands. At first, he doesn't realize, but then he remembers the cards covered in blood. Steve is holding one in his hand, before he kneels and lets it fall into the grave. It is signed.

Tony turns at that moment and stalks off. He hates funerals and he's not sure why he came to this one, since half the people there hate his guts or are at least indifferent to him, and the man they're burying was never very fond of him either. To be honest, he's not sure where his own fondness for the man came from, in-between interrupting his meetings and his dates and refusing to back down. He admires – admired – something in the agent and deeply regrets that he never had the chance to know him better. Of course, his own feelings about Coulson's death are all wrapped up in himself, and Tony feels a fresh stab of self-loathing.

If someone is calling him, he doesn't hear it over his angry inner monologue, and is only pulled out of it when a hand falls upon his shoulder. Startled, Tony spins around and is face to face with Bruce Banner.

Life has been… odd, since the Avengers. The whole Avengers fiasco was odd in and of itself, but it is the repercussions of that day that stay with Bruce. Life has changed since then.

Most of it – well, he'll say all of it – is thanks to one man. Tony Stark. Bruce imagines that if Tony hadn't been on that helicarrier, events would never have played out as they had. He's not sure how they both became so endeared to the man, but the fact remains that Tony was the driving force behind Bruce returning to the field, behind the Hulk managing to work with a team. In the aftermath, when he was told about how close Tony had come to dying and how the other guy had saved him, he began to wonder if Tony had been right all along. From that thought, came two realizations: the Hulk was capable of more than destruction; and Tony was a very rare kind of person, the kind who could earn the other guy's respect.

Bruce feels more at peace with himself than he has in his whole life. He is beginning to understand his nature, and the Hulk's, and learning how to balance both. He never forgot Tony's words to him about the terrible privilege, or the sight of that blue light radiating from Tony's chest. Though he doesn't fully have a handle on it yet, he's getting better at appreciating that Hulk might have a purpose in this world.

When Tony approaches him at the funeral, he smiles a little, glad that whatever small bond they'd forged before wasn't gone after the end of that day. When Tony nudges him, he has to restrain a laugh. There are no words for how much he appreciates how naturally Tony treats him. Most people tip toe around him, trying to act natural but always on edge, nervous. Tony is so completely relaxed around him that it's almost stupid – but as history has shown, both Bruce and the other guy are fond of him, so perhaps he'll be fine.

After the funeral, Tony turns and storms away so fast Bruce's head spins. The man turns, sees Tony stalking away with his long coat trailing behind him, and before he realizes what he's doing he's running after him. He's not sure what he'll say or do, but he can't just stand there and watch him leave.

Bruce calls for Tony as discretely as he can – this is a funeral after all – but the man either doesn't hear or doesn't heed him. So he catches up to him and puts a hand on his shoulder, tugging lightly to get him to turn around. When he does, Bruce meets his eyes. There's a look there, a soreness like a wound that hasn't healed, but it vanishes before Bruce can blink.

"Bruce, hey, how're you? Still living on the run? How is 'cave, sweet cave'?"

Bruce smirks at him, noticing the distraction for what it is, but he doesn't pry. "Just fine. I even drew a cave painting of you on my wall to remember all the fun we had together."

"Hopefully I am very dashing, as far as stick figures go."

"Of course." He's grinning now, and he feels a little guilty since the mood had been so somber a moment before. But he realizes that Tony needs this, this levity, so he allows himself to goof off a little. "And how've you been?"

"Oh…" Tony leans back, letting out a huff of air. "The usual, you know. Building things, destroying things, living in a huge, empty mansion all by my lonesome… y'know I should really look into fixing that, I mean, I use so little space – maybe I could rent out some rooms, start a motel –"

He knows where this is going. "Tony."

The billionaire's face is the picture of innocence; he throws his hands out like he's surrendering. "Just a thought. Suggestion. Planning out loud. Y'know, at this hypothetical motel, I could totally build some rooms for relaxing, or smashing, letting out steam –"

"Tony."

"We could call it the 'Green Room'-"

"Building a motel and letting me rent one of the rooms would be the worst idea."

"You know, you're absolutely right," The look on his face is almost calculating, but it's still playful. "Which is exactly why I'll just build you your own wing of the mansion, complete with Smashing room and a state-of-the-art lab –"

Bruce sighs as Tony rambles on, feeling both exasperated and touched by his friend's persistence. "Really, Tony, I can't –"

"Sure you can." His tone is a little more pleading now. "You could at least try, for a while. Give it a test run. … Please."

Until that last moment, that last word, they'd been talking as usually, even goofing around a little. But Tony Stark never says Please, ever, and that word sends a thrill of shock through Bruce. With narrowed eyes, he examines his friend's face. Tony is trying to hide a wince, obviously not having planned to ask nicely and a little embarrassed that his polite side had slipped out… or something similar to that.

There's something in his tone, something in that word, that makes Bruce think of the situation differently. Before, it was just Tony testing fate, trying to get him to go along with his crazy schemes. But now he's said please. And now, Bruce staying at the mansion means something different, something… something he's not sure he understands just yet. But there's only one way to find out.

"All right," Bruce mumbles his voice low and dry. "All right. One try. The first hiccup and I'm gone."

Tony's face lights up like the sun.