A/N: Written for the Halloween prompt at the Hulkwidow Network's Four Weeks of Prompts.

No Masquerade

Cap didn't spend a lot of time in the lab. Bruce thought that probably had at least as much to do with the fact that Tony did as with the fact that Steve was a soldier, not a scientist. As this rare appearance in the lab coincided with one of Tony's absences-he was down in SI today, textiles division-the hypothesis seemed to have proved correct.

"Can I do something for you, Cap?" Bruce asked as Steve strode in with that demeanor that never looked uneasy with his surroundings, even if they weren't his usual ones. Although he did glance around before answering. Double checking for Tony? He carried a tablet in one hand.

"If you've got a minute. I don't want to interrupt"

Bruce pulled off his glasses, folding the earpieces as he stepped away from his workstation. "I was just about to take a break."

He wasn't, really, but he wasn't getting much done, so he might as well. He could use a distraction from the distraction of Tony's textile project.

"Take a look at this." Steve placed the tablet on the desk, cued up to YouTube.

"Normally it's Tony interrupting my work to show me cat videos."

"This one isn't cats."

No, it definitely wasn't, Bruce saw as he put his glasses back on and bent to get a closer look at the small screen, where a man challenged random people on the street to pick up a homemade Mjölnir. When they couldn't, he blew their minds by picking it up himself.

"Electromagnets and a fingertip reader," Bruce said, chuckling. "That's a pretty clever prank. Did you show this to Thor?"

"Not yet." Steve closed the tablet's leather case. "Actually I thought it'd be more fun if he didn't see it on YouTube." It was obvious where he was going with this, even before he said, "But I'd need help making one."

"Guess that answers who you're going as for Halloween," Bruce said.

Tony, inspired by the cast of Breaking Bad dressing as other characters from the show at wrap parties, declared that the whole team should dress up as he each other for the Avengers Halloween party. For once, everyone thought this was a great idea. Except for Bruce, but he kept that to himself, because he couldn't in good conscience protest when Cap and Tony were actually in agreement on something.

"And Thor's going as Captain America," Steve replied.

"I guess you two can just trade clothes, huh? You're both…" Specimens. "About the same height and..." He swallowed. "…build."

"But it's kind of unfair he can carry my shield when I can't lift the hammer. Can't you just imagine his face? If we can make our Mjölnir look realistic enough, it'll be a hoot."

Bruce could all too easily picture the God of Thunder looking perfectly…well, thunderous, and chuckled at the mental image. "I have to admit, Cap, you never really struck me as the prankster type."

"Well it is trick or treat," Steve said, "and Stark's parties are never lacking in treats, so…"

Bruce rubbed his chin. "He's more your design guy, though." So much for distraction from what Tony was up to in SI…

"But you're the more discreet guy."

"Well, one of me is," he joked, but when Steve didn't look amused he moved swiftly right along. "If I help with your costume, does this get me off the hook wearing one?"

"And leave us an incomplete set? Don't let the Avengers down, Dr. Banner," Steve said, and patted him on the shoulder.

The Mjölnir project kept Bruce occupied for the better part of two days. Tony was still working on his project in SI, leaving the workshop free. It made for a nice change of speed and scenery, if only Bruce didn't think about why the workshop was free for him. Luckily, the challenge of designing a hammer that might fool the actual Mjölnir's owner kept his thoughts occupied.

As expected, the engineering wasn't the most difficult part (although he did make a few improvements to the original design, which he smugly toyed with contacting the YouTuber about); getting the Norse knotwork and the heft right was, when neither of them could pick the thing up. But a couple of stealth pics snapped with Steve's phone, along with some SHIELD footage of Thor in action gave Bruce an educated guess of the weight based on the velocity of the swing and impact damage-although Asgardian strength was another variable to account for-and he was reasonably pleased with the results in the end.

And back to fretting. About several things. The chief one being how stupid was going to look dressed up in the leather gear Tony dropped onto his workstation, without any regard for the actual work Bruce had spread out on the desk.

"Try to look a little more excited, will you?" Tony said, gripping Bruce's shoulder as he eyed it dubiously. "This is a cosplayer's wet dream. It's the Hawkeye fabric, engineered by Stark Industries, custom-tailored for you."

"I guess I should just be glad you didn't give me a Black Widow costume."

Tony's hand fell to his side. "Bruce. I love you, but the only one of us who has the figure to pull the catsuit off is-"

"Natasha."

For a full five seconds, Tony's mouth hung open, and he stared without blinking. A long time not to make a comeback-for him-but not long enough for Bruce to formulate how to extract himself from this inevitably awkward conversation before Tony recovered his ability to run his mouth.

"Okay. I was going to say me, but. Your response is intriguing." He hopped up to perch at the edge of the desk. "Tell me more."

Bruce turned away, pulling off his glasses to rub the bridge of his nose as he was assailed by a sudden onset headache.

"And Cap says I'm the discreet one," he muttered.

If Tony didn't spare Bruce any embarrassment over his little Freudian slip, at least he gave him the dignity of a Hawkeye costume that didn't leave him bare-armed.

"You can model the new winter suit I designed for him," he said, without a trace of his usual irony.

"I never imagined my life turning out this way," Bruce said in tones of unbelief, which Tony interpreted to be wonder.

Sleeves were something to be thankful for, though, and by the time the Halloween party rolled around, Bruce's worry about how stupid he'd look in costume gave way to worry about which of the remaining Avengers would show up in a Hulk mask: Barton or Natasha?

And which was worse?

AC/DC blared over the lounge speakers as Barton entered, dressed in one of Tony's suits-as in Armani, not Iron Man.

Natasha. The answer to which was unsurprisingly, infinitely worse, was Natasha.

"So we're waiting on Romanoff?" Tony gave one of the long spiral curls of his auburn wig a huffy flick over his shoulder. "She's not even coming as a girl and she's the last one to be ready."

"You know, usually we're all standing around waiting for you to finish primping," said Cap, sporting flowing locks of his own beneath Thor's helmet.

"Yeah, but I'm slightly more understanding of that now that I'm wearing a five thousand dollar bespoke suit," Barton added with a glance in one of the many reflective surfaces in the lounge.

Tony ignored them and adjusted the hang of the quiver strapped to Bruce's back. "It never takes you this long to go green."

Bruce was so expectant for green that it didn't register immediately that the petite, bespectacled brunette approaching the group at the bar, wearing a lab coat over a purple button-down and khakis, was her.

"For two frequently undercover operatives," Tony said, "Romanoff and Barton are real disappointments in the costume department."

He stalked off in his knee-high boots, leaving Bruce alone with his doppelgänger.

Natasha's green eyes peered up at him expectantly from behind the lenses of the wire-frame glasses. As he cast about for something to say, his heart raced, and he reached up to rub the back of his sweaty neck in a decidedly unHawkeye-like gesture. She looked cute, the white coat not fitting her as well as her own clothes (had she actually borrowed one of his?), the short shaggy wig giving her a pixie look, but didn't it sound a little narcissistic to say that to someone who was dressed as you?

"No one told me we could come as our non-superhero identities," he said, instead, lamely.

But she gave a wry grin as she shambled around the bar, hands shoved deep into the labcoat pockets. "Personally, I'm relieved Stark's not prancing around in the leopard-print dress and stilettos I wore to his birthday party a few years ago. I don't even want to know how he knows my exact shade of lip color."

She wasn't wearing any tonight, or if she was, it was neutral, like the rest of her makeup to accommodate the Dr. Banner look. Which was exactly the sort of detail-oriented thought that had gotten him into trouble with Tony.

"Dolce and Gabbana Classic Cream Lipstick in Devil!" Tony called from where he and Barton were in conversation across the room.

"It's like living with Big Brother," Bruce said, turning to face Natasha across the bar. "He had all my measurements for this."

The breathability of the engineered fabric was put to the test as she studied the details of the costume, eyes lingering on the sleeves.

"It's Barton's new winter look," he hastily explained. "I have a new appreciation for how the rest of the guys go out in these and feel confident and badass. Speaking of appreciation…thanks for not coming as the Other Guy."

"By Odin's beard! What sorcery is this?"

Knowing perfectly well what was happening behind him, Bruce watched Natasha's eyebrows pull together before he turned to see Thor flummoxed by the fake Mjölnir, which he couldn't lift from the stainless steel coffee table, despite the bulging of his muscles against the fabric of the star-spangled suit indicating he was trying very hard to do. Somehow even in Asgardian garb Cap looked as smug as he ever did when he won an argument with Tony as Thor relinquished the hammer to Barton and Tony, who were equally conquered.

"What's the matter?" Cap taunted, lifting it easily. "Not worthy? I can't be the only one?"

"It's a trick," Barton said.

"I call it a treat," said Natasha.

"This is Banner's sorcery," said Tony.

Bruce grinned, "Actually, I can't take all the credit. It was this guy on YouTube…I just made a few improvements."

"This is why I wore a labcoat," Natasha's rasp drew his attention back to her. "You're a superhero."

"I…" Bruce grinned dopily at her as she bent, as though retrieving something from the cabinets below the bartop "That's…Thanks."

Natasha straightened up, lifting her hands, which were now encased in a pair of green foam Hulk hands.

"Couldn't resist," she said.

Bruce laughed. That Natasha made him feel enough at ease about the Other Guy to do so was hands down the cleverest trick of the party.

A/N: While I'd love to take credit for the prank in this fic, I was inspired by a real-life prankster extraordinaire. You can find his video, "Real Mjolnir," on YouTube. Marvel fans are just the best! Especially my beta reader, malintzin, and all of my readers! Happy Halloween!