Natasha and Clint marry just as stealthily as they do everything else.
Tony’s first hint comes a couple months after Natasha gets out of the hospital after a close call with the latest SHIELD enemy. An elaborate scheme to get Tony to build her her own arc-reactor, he accuses her later. Instead, he builds her a suit of armor – smaller and significantly less awesome than his own. She refuses to wear it, whining that it’s too conspicuous. Tony thinks it’s less conspicuous than a gaping chest wound. And he should know.
Natasha heads back to the field, sneaking off to lie to someone or get lies out of someone, or lie about lies, all that fun lying stuff.
Tony sneaks into her bathroom and takes copious advantage of her skincare products. She doesn’t pay rent, so technically she owes him. Pepper told everyone the one time he used hers. Thor didn’t understand, but Steve, Clint, and Bruce thought it was hilarious and amused themselves impugning his masculinity for the rest of the day.
He finds the object next to the sink: a single gold ring hooked over the tail of tiny silver cat figurine. Weird. Natasha doesn’t wear much jewelry unless her cover requires it. Once she tried to garrote Tony with a necklace, though, so he’s okay with it.
He’s never noticed her wearing it, either, but it’s not like he looks at her hands all that often. She has other, more appealing body parts.
Some other stuff happens around this time that Tony only connects later.
Thor shows up with a bunch of runes tattooed on his ass. He excitedly shows Tony, and the rest of the house, by bounding around the house completely naked. Thor tries to explain what they mean, but it doesn’t really matter, since as far as Tony knows it means a giant immortal ass waggling in his face first thing in the morning. He sets up a new security protocol to keep rampaging naked Gods out of his room.
Later, Thor wants to know if The Other Guy would show up if Bruce got a tattoo.
“I don’t know,” Bruce says, and shrugs. “I don’t want a tattoo. Especially on my ass.”
Tony pokes him in the arm with a pen, and nothing happens. “I think we’re good,” he says. “Want me to hold him down, Thor?”
Bruce backs away and locks himself in his lab, because he is no fun.
Then Steve starts asking his usual questions about American society since he became a Popsicle. This time, he wants to know if marriage is still a thing.
“Yeah,” Tony reassures him. “Marriage still exists. As does divorce, fortunately.”
Steve doesn’t seem satisfied, not even when Tony tells him premarital sex is allowed now. “And gay stuff, too,” Tony offers, which makes Steve turn bright red. “Whichever one you’re thinking about doing," Tony warns, “prenup. Make sure you get one of those.”
“I’m not getting married,” Steve says. “I wouldn’t even know how,” he trails off. Tony thinks he might have been watching too much The Bachelor.
“I know how!” Thor says, excited because he can’t usually contribute to these conversations. “You go the place of governance,” he tells Steve, earnestly. “You and your beloved take vows before a man of the justice and the peace.”
Tony squints at him. “That’s not insanely wrong,” he says, confused.
“With a witness,” Thor continues, “who signs the parchment and promises to tell no one. This is an honored task.”
“Why can’t you tell anyone?” asks Steve, looking baffled and a little sad.
“None of that serum made it into your brain,” Tony says. “Not even a drop of it, huh?”
Steve glares at him and Thor glares at him, but he doesn’t care, because they’re both idiots.
“I’m going to…” Tony trails off, outraged. “How dare they?” He looks at Thor, who blinks back at him innocently. “You? They told you?”
“It is an honored task,” Thor repeats, puffing out his chest.
“What are you talking about?” Steve asks.
“Agent Barton,” Tony seethes. “Denied me the chance to throw him a bachelor party. I am going to kill him.”
“What?” Steve asks. “Clint got married?”
“I told no one,” Thor insists, looking violated. “I vowed on my honor. I vowed on Mjolinar.”
“He married Natasha, right?” Steve checks. Tony looks at him. “I notice things, too.”
“I told no one,” Thor says again. He rises and all that’s missing is a petulant hair toss.
Tony can’t stop ranting. He’s on to the part about the strippers denied livelihood by keeping this private, when Bruce reemerges from his lab.
“He found out,” he says to Thor.
“You knew, too?” Tony is going to have an aneurysm.
“Thor asked me about appropriate wedding gifts,” Bruce says. “I had to tell him no corpses of any kind.”
“I told no one,” Thor repeats.
“You don’t know that many people,” Bruce says.
“Natasha!” Tony bellows, storming off towards her room. “Mrs. Clinton Barton! Mrs. Barton, come out here!”
“Is she going to like that?” Steve whispers behind him.
“No,” says Bruce.
“You must tell them I said nothing,” Thor says.
Natasha is in the shower, when Tony barges in and swipes her cat ring-holder. He holds it up. “Exhibit A!”
The shower curtain pushes back and Clint’s wet head pokes out. He stares at the four men crowded in the bathroom door.
“Oh,” Tony says. He spins the ring around on the cat tail. “I’ll just let you and the missus finish, then. “ He turns around and leads everyone out.
“I told no one,” Thor tells the curtain as it slides closed.
They can’t hear any voices from inside the bathroom. The stealthy couple has left the shower running, and possibly they’ve climbed out the window. Tony imagines naked Natasha crawling up the side of the Stark tower and is distracted for a little bit.
But then the door swings open and Clint and Natasha walk out. Wet, wrapped in fluffy white towels, and looking none the less lethal.
Tony crosses his arms and blocks the hallway. “Well, well,” he says.
Natasha looks about as annoyed as she always does. Clint has trouble keeping his towel on his hips, nearly giving them all a glimpse of more marital equipment.
“What do you have to say for yourselves?” Tony demands.
“I want locks installed in the bathrooms,” Natasha says.
“From the inside,” Clint adds.
“Are romantic unions permitted in the bath?” Thor asks, sounding curious. Steve is turning red again. Bruce tries not to grin, fails.
“Union is permitted anywhere you can both get your pants off,” Tony snarls. “But city hall? Really?”
“They wore pants,” Thor says. “But I told no one,” he reminds Clint and Natasha. “I kept my vow.”
“Thank you, Thor,” Natasha says, sounding mostly genuine.
“Too bad we didn’t have him vow to hit anyone he hasn’t told with his hammer,” Clint says.
Tony has zeroed in on Clint’s left hand, hitched around his towel. There’s a black…thing on it.
“A ring tattoo,” he says. “Are you a goth rocker from the 90’s?”
“The weight threw off my aim,” Clint replies, clearly visualizing shooting Tony.
“Oh, well.” Tony glares some more. “That’s romantic.” He’s trying for snide, but it’s not really working.
“May I have my ring back?” Natasha asks.
“Give me your hand,” Tony says.
Suspiciously, she extends her left hand, hitching her towel up with other. Tony takes her wrist and slips it easily over her damp skin.
“With the powers vested in me, by me, before these witnesses, one of whom is actually a God, I now declare you man and wife, sniper and spy, long may you both live, and kill.”
Tony grabs Clint’s left hand and fits it into Natasha’s. “There,” he says. “Was that so hard?”
Clint struggles to hold his towel up one handed.
“I’m sending you both belated strippers,” Tony warns them, and stomps off.