A/N: My WinterIron Spring Fling gift for Finely Honed (jaqen_hgar) on Archive of Our Own, who wanted a story where Bucky is convinced Tony and Natasha are an item, Tony is crazy about Bucky but oblivious his feelings are reciprocated, and Nat knows what's up and does her best to push Bucky's buttons in an attempt to get the two idiots together. I hope you like it! :D

(A very special thank you to followthemuze for being an amazing beta and angel. )

~May the Best Assassin Win~

Bucky took a deep breath and wiped his sweaty palm on his jeans, checking his reflection in the mirror for what was probably the twelfth time in the last twenty minutes.

He could do this. He was a battle-hardened assassin who had stared down Nazis, aliens, and that weird, creepy tentacle thing Thor's ex-girlfriend had sicced on them all last week - he could ask Tony Stark out without throwing up, no matter what his stomach was telling him.

Because after months of struggling with his growing feelings for Tony, of wanting and pining and hoping, Bucky had finally been given a sign that his feelings might not have been quite as unreciprocated as he'd originally thought.

It had been just earlier that day, while Tony had been working on Bucky's arm.

Thanks to all of Tony's little tweaks making it run smoother, the arm rarely ever needed maintenance these days, but the latest threat to New York - an honest-to-God fire-breathing dragon - had left the skin along the metal seam of Bucky's shoulder puffy and tender, with a painful burning sensation that made it hard to move. Tony had thought it might have been a burn from the metal touching his skin, but had offered to look at it anyway, and Bucky - always eager for any excuse to spend time with Tony - had taken him up on it.

It had turned out to be burned, just as Tony had suspected, but Tony had had some sort of cream that he'd said would help with the irritation.

"Leftover from my arc reactor days," he'd explained, rubbing a generous amount into the skin around the metal. "I'll set you up with a jar. It's antibacterial, and I know you super-soldiers claim to be resistant to, well, everything, but every little bit helps."

Bucky had only been able to nod, too busy willing certain areas of his body not to get too excited by Tony's proximity, and then ended up shuddering anyway when Tony rubbed a particularly sensitive spot.

"Ah, sorry," Tony had said, moving his hand away immediately. "I probably should just let you-"

"No," Bucky had rasped, grabbing Tony's wrist before he could think better of it. And then Tony had looked up, his face just inches away from Bucky's, mouth parted and right there. Bucky had felt another shudder make its way down his spine, and then he'd found himself leaning forward, eyes on Tony's mouth, heart skipping when he realized Tony wasn't moving away -

The clatter of the jar of cream hitting the floor made them jump apart.

"Hell," Tony had hissed, face red as he bent over to pick it up. "I'm sorry, I wasn't paying - uh, you know what? I'm going to go get you some more. You just… yeah," he'd squeaked before scampering off to another corner of the workshop.

Bucky had taken off before he could come back - too terrified and embarrassed to stick around - but after a few hours of wallowing in self-pity and replaying the whole incident in his head, he'd had an epiphany:

He'd almost kissed Tony. No, scratch that - he'd almost kissed Tony, and Tony had almost kissed him back.

Bucky didn't think he'd imagined it - there'd been a spark of something in Tony's eyes, and whatever it was, it hadn't been rejection.

"JARVIS, where's Tony?" Bucky asked, clearing his throat and - once again - checking his reflection. Maybe he should put on a different shirt, something sleeveless. Tony always seemed to appreciate his biceps.

"Sir is currently in his bedroom," JARVIS answered, surprising Bucky. It was only eight o'clock, and Tony was almost never in bed before midnight, if he could be persuaded to go to bed at all.

"Oh, is he… did he go to bed?" Bucky asked, swallowing down his disappointment.

"Sir is not sleeping, no." JARVIS replied, making Bucky frown at the odd wording.

"Is he busy?" Bucky asked, biting his lip. He could wait until tomorrow to ask Tony, but he wanted to do it now, before his courage failed him and he managed to talk himself out of it.

"He… likely would not want visitors at the moment."

Bucky blinked, brow furrowing, and wondered if he was imagining the reluctance in JARVIS's voice.

"JARVIS, is he okay?" Bucky asked, becoming concerned.

There was another pause, and then, "Sir is fine, Sergeant Barnes. But he is with Agent Romanoff at the moment, and I don't believe he wishes to be interrupted."

Bucky froze, replaying the sentence in his head again, his stomach clenching unpleasantly.

"What is she doing in his bedroom?" he demanded, because no, they couldn't be. Could they?

"I highly doubt either Sir or Agent Romanoff would like me to disclose that information," JARVIS replied, sounding wary.

"What?" Bucky croaked, stepping back and plopping down on his bed, hard.

JARVIS made a noise Bucky would have called a sigh in human. "I'm afraid my privacy protocols prevent me from saying more, Sergeant Barnes. However, if you have a message you would like to give Sir, I can pass it on to him when he is less occupied."

Bucky swallowed and stood up, clenching his fist and shaking his head.

"No, JARVIS, I'll…"

He huffed and scrubbed his face, then took a deep breath. He was probably over-reacting. There were lots of reasons Natasha could be in Tony's room… occupying him. It didn't necessarily mean they were -

Nope nope nope, not finishing that line of thought.

"I'll talk to him later," Bucky said, rubbing the back of his neck.

"Very well, Sergeant Barnes."

Bucky sighed and started pacing the room listlessly, then changed into some workout clothes. Maybe heading down to the gym would help him get rid of some of his tension.

To Bucky's great displeasure, Natasha didn't leave Tony's room until early the next morning.

He knew this because he had ended up wandering up to Tony's floor instead of the gym, hanging around the hallway and telling himself that waiting to see when and if Natasha left wasn't at all creepy or stalkerish.

So besides being sick with jealousy, he was also angry and grumpy with sleep-deprivation, which was probably why he decided - rather unwisely - to confront Natasha about it that same morning.

"What were you doing in Tony's room last night?" he asked as soon as he found her in the kitchen alone. He tried to keep his tone neutral, but it ended up sounding more like something he would spit out at a captive HYDRA agent during an interrogation.

Natasha raised an eyebrow at him. "Sorry?" she asked, bringing her glass of juice to her lips and taking a sip, looking decidedly unimpressed.

Bucky gritted his teeth. "What were you doing in Tony's bedroom last night?" he repeated, clenching his fists

She cocked her head at him, eyes narrowed thoughtfully, before something like recognition flashed in her expression. Her mouth then quirked up in slow, devious smirk, making the hair on the back of Bucky's neck stand up.

"You're a big boy, you figure it out," she said, eyeing him carefully.

Bucky's stomach sank.

"So," he swallowed. "You two, uh, you're, you're a -"

Natasha's mouth twitched.

"Is there a problem, Barnes?" she asked lightly, hiding some of her expression by taking another sip of juice.

Bucky glared, resisting the urge to rip the glass out of her hand and dump it all over her. He was saved from actually following through with the impulse by the arrival of Steve, looking cheerful and a little sweaty from his morning run.

"'Morning, Nat. Buck, you're up early," Steve said, pulling some milk out of the fridge and then pausing, noticing the tension in the air. "Something wrong?" he asked, looking between the two of them with his eyes narrowed suspiciously.

"Nothing," Bucky bit out before turning and stomping out of the room.

The thing was, now that Bucky knew what to look for, he couldn't believe he'd never seen it before.

True, he'd noticed Natasha had seemed to have a soft spot for Tony, but he had thought it no more than fond friendship. She'd never implied otherwise, and Tony had never given any inclination that he was interested, either - or so Bucky had thought.

Clearly, he was an idiot.

Because now that he had seen it, he couldn't stop seeing it, either.

Sure, some of it was little things - like Natasha knowing exactly how Tony took his coffee, or knowing his schedule if one of the others asked after him - but there were also other, more obvious signs that were much harder for Bucky to ignore.

Like the pet names, for instance. With the exception of the fond way she called Clint 'idiot', Tony was the only person with whom Natasha used any terms of endearment. They were always in Russian, too, which meant Bucky knew exactly what she was saying, even if the others didn't quite catch on, and had to endure watching Tony huff while Natasha smiled fondly and called him 'kitten'.

They had their own private jokes, which, again, didn't happen between Natasha and anyone else besides Clint. There were times where Tony sought out Natasha specifically - or vice versa - and it wasn't unusual to find them curled up on the couch together, watching TV or conversing quietly.

Which brought Bucky to the thing that was really, really driving him crazy - the touching.

For Natasha - never a very tactile person, ordinarily - was constantly touching Tony.

She reached out and touched Tony when they walked past each other - a light, casual pat to his arm or a squeeze of his shoulder, both of which seemed to make the tension drop from Tony's shoulders, and never failed to make Bucky's jaw clench. She ran her hands through Tony's hair or over his shoulders when she passed by his chair, sometimes even stopping to rub at the exposed skin at the back of his neck. She got handsy with him when they sparred in the gym, lingering a few extra seconds when she corrected his posture and pressing up against him in a way that made Bucky's skin crawl.

And while it bothered Bucky when Natasha touched Tony, it was almost worse when Tony was the one who got touchy-feely. Like when he wrapped his arm around her and played with her hair when she curled up against him during movie night, or when he rubbed her feet when she planted them on his lap.

The thing that made it even more unbearable, though, had to be the smug looks Natasha shot him whenever she caught him staring at them. Like this morning, for instance, when he'd walked into the common room and found Tony fast asleep on the couch, his head in Natasha's lap and her fingers carding through his hair. Bucky didn't know what Natasha had seen in his expression, but whatever it was had had her looking like the cat that ate the canary. He'd had to go down to the gym and destroy three of Steve's reinforced punching bags to keep from screaming in frustration.

He was working on demolishing a fourth when Clint walked in and then froze, staring at the destruction with wide eyes.

"Bad day?" he asked, dropping his bag of equipment and whistling appreciatively when Bucky punched the bag hard enough to knock it off of its (supposedly indestructible) chain.

"Wanna spar?" Bucky asked instead of answering Clint's question, adjusting the wrap on his flesh hand.

Clint blanched. "While you're in that mood? Hell no. If you want someone to beat up, go find Steve. He's less fragile than I am," he said, tossing a towel over his shoulder and making his way over to one of the weight machines.

Bucky scowled. He couldn't actually work out with Steve right now, because then the punk would want to know what was bothering him and demand he talk about it.

Instead of saying that aloud, though, he plopped down on the mat nearest Clint and found himself asking "Did you know about Natasha and Tony?"

Clint wrinkled his nose. "Did I know about Nat and Tony what?" he asked, sitting down on one of the benches and inspecting a barbell. "If you're talking about how they've convinced Thor that Game of Thrones is a documentary about Tony's ancestors then yes, because I'm the one who suggested it. If you're talking about the 'God Bless America' patch they put on the seat of Steve's uniform, then no, this is the first I've heard of it."

Bucky shook his head and then bit his lip, staring at the ground. "No, I mean their… thing. You know, their Natasha-and-Tony thing," he added at Clint's blank look.

"You've lost me," Clint said, glancing over his shoulder at Bucky.

Bucky let out a frustrated huff. "Never mind. I guess that's a no, then," he said, standing and scowling at the corner with all of his destroyed punching bags.

Clint turned and cocked his head at him, frowning, before his eyes widened in realization. "Oh. Oh. Wait… you don't think they're dating or anything, do you?" he asked, looking at Bucky like he'd just sprouted another head.

Bucky flinched and then glared at him, because while thinking it might have been bad, hearing somebody else say it was infinitely worse.

Clint blinked, dumbfounded, before his expression morphed into something thoughtful. "Huh," he said, crossing his arms and leaning back. "I thought she was being extra touchy-feely with him in public lately."

"So I've noticed," Bucky ground out, clenching his fists.

Clint cocked his head again, watching him with a sort of laser-sharp focus that made Bucky feel as though he were seeing right through him.

"I guess it kinda makes sense," he said finally, his breezy tone at odds with the contemplative look he'd been giving Bucky a few seconds ago. "I suppose she kinda fits Tony's type..."

"And what type is that?" Bucky asked bitterly, squaring his jaw.

Instead of replying verbally, Clint gave Bucky a curiously intent look.

Not sure what to say to that, Bucky gathered his things and left the gym, wondering what it said about the situation if Natasha's own best friend hadn't known about it.

"Your hips are too tight," Natasha sighed, placing her hands on Tony's hips and moving up behind him. "You need to loosen up, or your movements will be too slow."

A sharp blow landed on Bucky's shoulder, making him twist to avoid another and forcing his attention back on Steve.

"Buck, come on. Eyes on me," Steve said sharply, gaze flickering between Bucky and the mats where Natasha was working Tony. "What's up with you today? You keep getting distracted."

"Nothin'," Bucky grunted, rolling his shoulders and indicating that Steve should continue. "Out of practice."

Which - technically - wasn't a lie. Bucky hadn't actually been to the gym since his talk with Clint three days ago (due in part to Steve finding out about the punching bags and banning him from any further use of them), and with his mood being what it was, he hadn't trained with anyone in well over a week, either.

Bucky could tell from Steve's expression that he wasn't buying the excuse, but he wasn't pursuing it, either. He did make a show of telegraphing his moves more, though, which Bucky might have found insulting if it hadn't made it easier for him to watch Natasha and Tony out of the corner of his eye.

As if sensing his gaze, Natasha looked up and locked eyes with him. She turned back to Tony and said something that made his face go red, then moved her hands down to his thighs.

Pain exploded on the right side of Bucky's skull as Steve clocked him in the face, hard enough to stun him and bring him to his knees.

"Buck!" Steve cried in surprise and irritation, but whatever else he'd been about to say was drowned out by Sam wolf-whistling from across the room, drawing both Steve and Bucky's attention.

"'Tasha, come on!" Clint - Sam's sparring partner - groaned. "If you're going to feel up your boyfriend, can you at least do it in private? You're supposed to be teaching him how to block, not giving us a peep show!"

Tony startled and looked up, inadvertently stepping out of Natasha's reach, to Bucky's immense relief.

Natasha sighed and raised an eyebrow at Clint. "If you think you're a better teacher, you're more than welcome to take over," she said coolly, arms crossed.

Clint rolled his eyes. "I'm just saying - just because you two are an item now doesn't mean you can use team training as an excuse for foreplay, okay? My delicate sensibilities can't take it," he said, making a face.

Steve made a noise from beside Bucky - either to catch Bucky's attention again, or to scold Clint - but Bucky was too busy watching Tony's reaction to pay him any mind.

Because Tony actually looked… confused.

Tony wrinkled his nose. "What are you talking about?" he asked, at the same time Natasha scowled and said "Clint…"

Sam held his arms up. "Wait, hold the phone - you guys are dating?" he asked, eyebrows raised in disbelief.

Tony nearly dropped his water bottle. "What? No - where the hell would you get that idea?" he demanded, before turning his glare on Clint. "Stop spreading lies, Birdbrain. Nobody likes a gossip."

Hope swelled in Bucky's chest. "You mean you two aren't together?" he blurted out before he could think better of it, drawing everyone's attention.

Natasha's face went carefully blank, but Tony's brows knitted together. "Of course not!" he exclaimed, giving the room at large an irritated look. When his eyes settled on Bucky, though, they looked almost hurt. "Why does everybody keep saying that?"

All eyes turned to Natasha, who shrugged nonchalantly. "Ignore them, kotenok," she said, giving Tony a sympathetic pat on the back. "The children just like pulling on our pigtails."

She then looked over at Bucky, raised one eyebrow in challenge, and kissed Tony's cheek.

Bucky saw red.

"How about I take over Tony's training for a little while?" he said loudly, cutting off Clint and Sam's sounds of protest.

"Uh, Bucky?" Steve started, picking up on Bucky's ire.

Bucky ignored him and stomped over to Natasha and Tony, making sure to show lots of teeth when he smiled at her.

"Does that sound okay to you?" he asked, voice softer as he directed the question at Tony.

"Um," Tony replied, uncharacteristically flustered. He then glanced helplessly at Natasha, making Bucky's stomach sink.

"How about a demonstration, instead?" Natasha suggested, eyes glittering dangerously.

Bucky had a feeling he knew where this was going, and wholeheartedly approved. "What kind of demonstration?" he asked, noticing Tony backing up and the others getting closer.

Then Steve walked over, looked between the two of them, and coughed pointedly. "Maybe I should take over Tony's training," he began, only to clamp his mouth shut when two sets of deadly glares settled on him.

"Three matches, the normal rules," Natasha sniffed, turning her attention back to Bucky.

Bucky considered her. "First blood?" he suggested, ignoring Steve's indignant splutter.

"Most hits," Natasha decided. "Steve can be referee," she added, making Steve throw his hands in the air.

"What the fuck is happening right now?" Sam muttered, sounding equal parts awed and terrified.

"Who cares? Twenty bucks on Nat," Clint hissed back, elbowing him and then Tony, who, like Steve, was looking increasingly alarmed by the proceedings.

Natasha caught Bucky looking at him and, smirking, raised her chin in challenge.

"Jealousy is an ugly color on you," she said in Russian, her grin turning predatory. "Lets raise the stakes - winner gets to kiss Tony."

"Deal," Bucky replied, shifting his stance. "But the loser has to leave him alone for a week. No touching."

Someone made a strangled noise, and when Bucky looked over to find the source, Tony was staring at him, eyes wide with both wonder and hope.

"Agreed," Natasha said, switching back to English.

It was all the warning Bucky got before she launched herself at him, flipping over his arm when he tried to block her and driving an elbow into his stomach.

"Forty bucks on Nat!" Clint yelled while Bucky wheezed.

Bucky made a mental note to throw Natasha into him the first chance he got.

Three rounds, one hour, two possibly cracked ribs, and a busted lip later found Bucky staring at the ceiling while lying on his back, breathing hard and basking in victory.

Well, okay, a draw wasn't a victory. But it wasn't a loss, either, which was all Bucky cared about at the moment.

"Steve, come on, that last hit didn't count - he threw her into me!" Clint protested as he followed Steve and Natasha out of the gym, Sam trailing behind them, whistling cheerfully now that he was sixty bucks richer.

A shadow fell over Bucky as the only other occupant of the room bent over him, face pensive.

"Are you alright?" Tony asked, brow pinched in worry.

Still too winded to speak, Bucky nodded and gave him a thumbs up.

Tony sighed in relief, then surprised Bucky by sitting down beside him and handing him a water bottle, which Bucky accepted gratefully. After a few minutes of sitting in silence, Tony cleared his throat and glanced sideways at him.

"So," he said, in slightly accented Russian. "Does a draw still warrant a kiss, or are you not allowed to touch me?"

Bucky choked on his water.

"You, uh, you speak Russian?" he said calmly after a few seconds of coughing, face flaming as he tried to remember what exactly he and Natasha had said before and during the match.

Tony nodded and covered his mouth with one hand, eyes shining. "Were you… have you really been jealous of Natasha?" he asked, voice muffled by his hand.

Cheeks burning and unable to look Tony eye, Bucky went back to staring at the ceiling.

Bucky heard the mat beneath them shift, and then Tony leaned over into his line of vision again, looking positively elated.

"Well I, for one, think you're entitled to a consolation kiss," Tony said, nodding seriously and trying - and failing - to school his expression. He then slowly placed his hand on Bucky's chest, splaying his fingers loosely over Bucky's heart.

Bucky swallowed, putting his hand over Tony's and pressing down, so Tony would be able to feel how fast his heart was beating.

"Only if Natasha doesn't get one," he rasped, sitting up at the same time he tugged Tony down towards him, and swallowing up Tony's startled laugh.

"You seriously thought me and Natasha were together?" Tony asked much later, folding his arms across Bucky's chest and propping his head up on them.

Bucky's 'consolation kiss' had turned into two, which had turned into three, which ended up becoming a thirty-minute make-out session on the gym floor. Bucky knew he probably should have been more embarrassed by the location, but as he currently had a lapful of pliant, happy genius, he couldn't really bring himself to care.

Bucky sighed and slid his hand into Tony's hair, feeling pleased when Tony leaned into the touch.

"She spent the night in your room," he pointed out, scratching at Tony's scalp and basking in bone-deep satisfaction when Tony practically purred.

"Mmmm-hmmm. So does Bruce, sometimes. And Rhodey, if I'm having a bad night when he's in town." Tony sighed, watching Bucky with half-lidded eyes.

At Bucky's questioning look, Tony sighed again and sat up a little straighter. "It's a thing Rhodey and I used to do when we were in college, and he knew I was feeling down. We'd eat ice cream and stay up all night watching movies, and he never cared if I got a little, uh, cuddly," he coughed, his ears turning an adorable shade of pink. "I started doing it with Bruce when he was having a rough night, and then Nat found out about it, and, well." He shrugged, the blush deepening. "She's a good snuggler. And she has a sixth sense for knowing when I'm upset."

Bucky let his head thump back against the floor, and somehow managed to tamp down the growl that was fighting to escape his chest. "Funny how she neglected to mention any of that when I asked her about it," he groused.

Tony squirmed. "Ah, well… since I'd just spent the whole night complaining about my feelings for you, I guess that's understandable," he mumbled, hiding his face in Bucky's shirt.

Bucky scowled at the ceiling. "That woman played me like a fiddle," he grumbled, though he was finding it harder and harder to stay angry, especially when Tony's hand snaked under his shirt.

"I know," Tony said happily, moving up until his mouth was hovering over Bucky's. "I'm going to buy her flowers."

Bucky grunted and rolled them over, and they didn't speak of Natasha - or much of anything - for a long while.

When Bucky finally returned to his room later, there was a card taped to his door.

The front had the words 'I'm sorry' and a frowny face on it, but inside there was only one line written in Russian, followed by a smiley face.

Hurt him, and you will die a slow and painful death. :)