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Lines We Were Never Meant to Cross

Summary:

Undercover work blurs lines. Peggy Carter insists she knows exactly where hers are.

Assigned to repeated missions that require fake relationships, practiced affection, and kisses meant only to sell a cover, Peggy and Natasha tell themselves it's professional, necessary, even.

But practice has a way of becoming habit. Appearances start to matter. And somewhere between rehearsed intimacy and real jealousy, pretending stops being the hardest part. After all, it's just for the mission. Until it isn't,

Notes:

Hi hello

This fic came from a deep love of undercover tropes, mission-required intimacy, and the very specific Peggynat problem of "it's just part of the cover" turning into feelings no one is emotionally prepared for.

This is a slow-burn, chaptered story where each mission pushes the line a little further, fake relationships, practice kisses, jealousy, denial, and the gradual realization that maybe this was never as professional as they claimed. It's rated Teen for now; lots of kissing, yearning, and emotional tension, but nothing explicit.

Peggy is doing her best. Natasha knows exactly what she's doing. Make of that what you will.

As always, thank you so much for reading, I'd love to hear what you think

Chapter 1: Strictly for Appearances

Chapter Text

Peggy Carter has faced down HYDRA officers, rogue gods, and the weight of a shield that comes with expectations she never asked for. None of that prepares her for the simple, destabilizing fact of Natasha Romanoff’s hand resting at the small of her back as if it belongs there.

The gala is being held in a renovated Viennese opera house, all marble floors and glittering chandeliers, the kind of place that disguises brutality behind refinement. Peggy registers exits automatically, scans for threats, and notes the subtle bulge of concealed weapons beneath tailored jackets. Captain Carter's habits are constant and relentless. The shield may be absent, but the instincts are not.

Still, it is difficult to concentrate when Natasha leans in close enough that Peggy can smell her perfume, something subtle and warm, chosen carefully, deliberately.

“Relax,” Natasha murmurs under her breath, lips barely moving. “You look like you’re bracing for impact.”

Peggy keeps her gaze forward. “I am always bracing for impact.”

“That,” Natasha says, amused, “is precisely the problem.”

Undercover spouses. Fury had delivered the cover with a straight face, as though assigning Peggy to play the devoted wife of the world’s most dangerous woman was not a calculated act of cruelty. Five years married, deeply in love, inseparable. The kind of fiction that demands physical closeness and emotional ease, two things Peggy has learned to ration carefully.

Natasha, of course, has no such reservations.

They glide through the crowd together, Natasha’s touch confident, proprietary. To anyone watching, the Captain Carter, war hero, symbol, icon, has softened into something domestic, affectionate. Peggy hates how easily the act slips over her like a second skin.

They stop near a champagne table. Natasha takes two glasses, fingers brushing Peggy’s as she passes one over.

“Smile,” Natasha says lightly. “We’re very happy.”

Peggy lifts her chin. “I am capable of pretending happiness.”

Natasha’s smile sharpens. “I know. You just don’t enjoy it.”

Before Peggy can retort, Natasha’s fingers tighten subtly at her waist.

“Red tie,” she murmurs. “Third column. Watching us.”

Peggy doesn’t look. She knows better. “What does he need to see?”

Natasha turns fully toward her now, gaze intent. “That we’re real.”

Peggy exhales slowly. “Define real.”

Natasha’s eyes flick briefly to Peggy’s mouth. “Affection. Convincing affection.”

Peggy opens her mouth to argue, this is unnecessary, excessive, reckless, but red tie shifts closer, attention sharpened.

Natasha doesn’t wait for permission.

She cups Peggy’s jaw with practiced ease, thumb resting just beneath her ear, and kisses her.

It is meant to be quick. Strategic. Nothing more than a believable gesture.

Instead, Natasha’s lips are warm and sure, her grip grounding, intimate in a way that makes Peggy’s thoughts scatter. For a heartbeat, Peggy forgets the opera house, the mission, the eyes on them. For one dangerous moment, she forgets to pretend.

When Natasha pulls back, Peggy is left blinking, breath unsteady.

“There,” Natasha murmurs. “Perfect.”

Peggy swallows, jaw tight. “Was that strictly necessary?”

Red tie looks away, satisfied.

Natasha meets Peggy’s eyes. “Yes.”

They move again, weaving through conversations thick with implication and threat. Natasha stays close, fingers brushing Peggy’s arm, her back, the small of her waist, each touch calculated for the audience, but landing far too personally.

Peggy has led troops into impossible battles without flinching. This, this careful dismantling of her composure, feels far more dangerous.

Then Viktor arrives.

Then it happens.

He is handsome in the way predators often are, all charm and polished menace. His gaze slides over Peggy dismissively before settling on Natasha with interest that makes Peggy’s spine stiffen.

“I’m Viktor,” he says, extending a hand to Natasha. “And you are?”

Natasha smiles, dazzling and false. “Helen. This is my wife. Maggie.”

Peggy offers her hand. Viktor barely acknowledges it.

They talk. About shipments. About access. About violence disguised as commerce. Viktor’s attention never truly leaves Natasha, and Peggy feels it like a physical weight, an assessment, a challenge.

Eventually, Viktor leans closer, voice low. “Perhaps we could continue this somewhere more private.”

Natasha hesitates, just long enough to sell reluctance. Then she nods.

Peggy knows the playbook. She’s approved worse. Signed orders that send people she loved into far more dangerous situations.

That doesn’t make this easier.

Viktor kisses Natasha.

It is not lingering. Not intimate. A controlled, professional contact, Natasha is playing the role she has perfected over years of survival.

Peggy still feels it like a blow.

She looks away, jaw clenched, hands curling into fists at her sides. She has faced down tanks without fear, but this, this helplessness, this inability to intervene without blowing the mission, gnaws at her.

She is Captain Carter. She commands. She protects.

And yet she is standing on a balcony, forced to watch the woman she wants kiss someone else because it is useful.

The worst part is how instinctive the reaction is. How personal. How little it has to do with strategy.

By the time Natasha returns, the music from inside feels distant and wrong. Peggy is gripping the stone railing hard enough that she’s surprised it doesn’t crack.

“You’re angry,” Natasha says softly.

“I’m not,” Peggy snaps, too fast.

Natasha studies her, expression shifting. “You approved the approach.”

“Yes,” Peggy says. “That doesn’t mean I have to enjoy it.”

“Enjoy what?” Natasha asks quietly.

Peggy turns to her then, eyes bright with something dangerously close to honesty. “Watching him touch you.”

Natasha’s breath stills.

“It was part of the cover,” she says carefully.

Peggy lets out a short, humorless laugh. “That’s what you said about our kiss.”

The silence stretches between them, thick with things neither has said out loud.

“No,” Natasha says finally. “I said it was necessary.”

“And this wasn’t?” Peggy asks.

Natasha steps closer, voice low. “Not to you.”

Something in Peggy’s chest fractures. “I don’t think I can keep pretending this doesn’t matter,” she admits. “That you don’t matter.”

Natasha’s expression softens, something unguarded flickering there. “Then don’t.”

The gala continues behind them, oblivious. The world always does.

Natasha reaches for Peggy, not for the mission, not for show. Peggy lets their fingers thread together, grounding. 

“This one,” Natasha says softly, leaning in, “isn’t for appearances.”

Peggy meets her halfway.

The kiss is slower, deeper, unperformed. No audience. No cover. Just truth pressing between them like a promise neither is quite ready to define.

When they part, Peggy rests her forehead against Natasha’s, breath unsteady but certain.

“Well,” she murmurs, “that complicates things.”

Natasha smiles. “You’re Captain Carter. Complicated comes with the shield.”

Behind them, the chandeliers glitter. The mission continues.

But something irrevocable has already changed.