The first time it happens, Steve comes home after a grueling workout in the local gym to find Clint bleeding on the couch. All thoughts of a well-earned shower flee Steve when his horrified heart jumps out of his chest. In the back of his mind he supposes he should wonder how Clint got into the apartment, seeing as how Steve takes special care to lock all the doors and the windows. The rest of his mind is engaged in rushing to the injured archer and applying immediate pressure to the wound. Super strength can come in handy-in no time at all, the blood flow has been successfully stopped and the decorative blanket SHIELD left over the back of the couch when they assigned him a place to live has been put to good use as a makeshift bandage to ward off infection. They don't talk about the incident and the fact that a different sofa now resides in the living room on top of a strategically placed rug doesn't need to be mentioned.
Clint must have told Natasha about the look of shock on Steve's face when he found his unexpected house guest because no later than a week afterwards, Steve enters his front door with arms full of groceries and sees her lounging on the new furniture, watching him expectantly. The pink in his cheeks doesn't begin to express his discomfort. Back in his day, it was scandalous for an unmarried man and an unmarried woman to be in the same house without a chaperone. While she casually blinks at him, he stutters out something about going to the store. She stares pointedly at the paper bags clutched tightly in his arms. Knowing that he'll get around to eating the extra food eventually, he spins on his heel and goes down the stairs two at a time. He doesn't look back until he's safely astride his motorcycle and navigating the heavy afternoon traffic.
He should have expected the visit from Stark. The eccentric billionaire hated to be outdone in anything and sneaking into Captain America's apartment was an activity he was not about to let a couple of master assassins beat him at. Yet, for some reason, Steve still yelps in an undignified manner when he returns from the Laundr-O-Mat only to find his seldom-used laptop in the hands of the nosy inventor. Thankfully, Steve doesn't even know how to work the darn thing and so Tony's attempt to find blackmail-worthy material is utterly fruitless. Endless optimism undeterred by the electronic failure, Tony unceremoniously dumps the contents of Steve's closet into a pile on the bedroom floor and rifles through it before Steve even knows what's happening. Disappointed to discover that the Captain is as pure and righteous as he appears, Tony shows himself out, grumbling on his phone to a smug Natasha that she has twenty bucks coming her way because she won the bet.
By this point, a pattern has been set. Steve doesn't know much about Bruce but he does know that he's a scientist and scientists love patterns. Predictably, as Steve sets his take-out container on the countertop, there's a nervous cough and the low light of the kitchenette's single bulb reveals a slightly rumpled Bruce, looking equal parts embarrassed and excited. While Steve isn't sure he wants to know the reason behind that particular expression, he feels it impolite not to ask. It's only a little bit ironic, considering that Bruce's impromptu visit is in itself impolite. But in spite of that, irony or not, Steve inquires as to the reason for Bruce's sentiments. Half an hour later, Bruce is waving goodbye and Steve is still mulling over the unfamiliar phrases and unpronounceable words that comprised the doctor's lengthy explanation. To this day, he still doesn't know what it was that Bruce found so stimulating in the tiny apartment.
Some things never change. When Steve was growing up, the scent of freshly baked pie drew an assortment of creatures to the delicacy, from blue-winged flies and squawking birds to wide-eyed children and finger-licking men. Although, when Steve was young, he had never heard of a pie attracting a demigod. Then again, in this strange new century, anything is possible and he almost can't help the smile that curls his lips when he steps through his entryway. Thor is slouching at the kitchen table, huge frame causing the wooden chair to sag ominously, fork in hand. The pie pan is before him, though it is almost empty. Crunching the golden crust and slurping up the apples as loudly as he is, Thor doesn't notice Steve's arrival until a second fork drops into the tin. Looking up, he sheepishly meets his unwitting host's gaze and gives him a sugar-stained grin. Steve doesn't mind. He's actually relieved he managed to figure out all the knobs and buttons and dials and do-hickeys and whats-its on the oven in order to bake the delicious pie. They share what's left of the baked good and sigh in contentment at the treat's conclusion.
For several weeks, this cycle is repeated, albeit with variations, such as more than one team member being present at one time. Thankfully, no one has needed to utilize his living room as a temporary emergency room since the first incident that started it all. That's not to say that Steve finds the apartment in the same condition in which he left it. Stains that bear a striking resemblance to macaroni and cheese litter his ceiling. But when inquired about, the resounding answer is that a food fight has certainly never taken place in his lovely apartment. The generic décor that was chosen by SHIELD is slowly disappearing. Glass bowls, which have stood empty on a set of bookshelves since Steve moved in, are replaced with photographs of Thor at the zoo. Steve isn't sure when they were taken, or even who framed them in what he's been told are High School Musical frames, but he likes looking at them whenever he walks past. Bulky alphabet fridge magnets spell out silly messages on the appliance which needs to be refilled far more often than before, which is remarkable, given Steve's metabolism. The bland floor lamp is gone. There's no substitute offered and Steve knows that's because the lamp wasn't intentionally removed. His sharp eyes pick out the pieces of glass that the vacuum he's still getting used to hadn't been able to suck up.
No longer does he dread dismounting his bike and hiking up the stairs to his floor. A grin is already on his face before he even gets to the pick-locked door. Noises of all manner, ranging from crashes and splashes to muffled laughter spills out into the hallway from beneath the door crack and Steve often apologizes to his neighbors before stepping inside to the circus his apartment has become. If he could have found it within himself to resent them, Steve would have been distraught at their lack of decorum, disregard of social expectations and their blatant invasion into his personal space. But he has no such feelings of agitation and instead is rather pleased with the whole absurdity of it all. Gradually, he learns to look forward to the intrusions and reconciles himself to the fact that his living quarters are no longer his own.
He provides them with a stress-free, SHIELD-free, press-free environment in which to kick back and relax. Always full, his cupboards are an all-you-can-eat buffet. The droll furnishings he hasn't bother to get rid of make for excellent target practice. After a while, he can't imagine life without a secret agent tossing darts at the ridiculous figurines on his mantle piece, or a scientist leaning over the tub, which is filled with neon green sludge. He gives them a safe place to hang out and they give him an overabundance of amusement. It's a win-win situation and Steve has no intention of upsetting the symbiotic situation.