Dr. Aldric Faust stood before a wall of glass, his expression as unreadable as the machines surrounding him.

Beyond the glass lay the Osprey, strapped to an operating table, every inch of her body restrained by steel and synthetic bands. Electrodes snaked across pale skin, connecting to a tangle of monitors that displayed a symphony of vital signs, neural patterns, and brainwave fluctuations. The subject's eyes, once defiant, now fluttered in a haze of confusion, flickering between reality and the fractured dreamscape Faust had meticulously crafted.

"Increase the neural suppressant by twenty percent," he said calmly, his voice smooth and cold, like the first breath of winter air.

A subordinate, trembling but efficient, adjusted the settings on the console beside him. Osprey convulsed briefly, then stilled, her heartbeat slowing to a languid, almost unnatural rhythm. Faust watched with clinical precision, eyes never leaving the woman's face as a sick smirk rested on his lips.

"Excellent," Faust murmured, his thin lips curling into a satisfied smile. "Now, let's see how deep the final conditioning has taken root."

He stepped closer to the glass, pressing a button on a small remote in his hand. The operating table slowly tilted upright, bringing Osprey's face level with his own. Her eyes, once vibrant and full of life a long time before she had been taken into the facility, now stared vacantly ahead as she awaited orders.

"Osprey," Faust called out, his voice carrying a hint of anticipation. "Identify your mission."

For a moment, there was silence. Then, Osprey's lips parted, her voice a hoarse whisper. "To serve Hydra. To eliminate threats to the new world order."

Faust nodded, his excitement barely contained. This was the final test - almost three years of experiment after experiment and it was almost time to prove that he had been right about his hypothesis. 

"And who are the threats, Osprey?"

"The Avengers," she replied without hesitation, a flicker of something—anger? pain?—crossing her face before disappearing. "They are the enemy. They must be destroyed."

"Very good," Faust purred, turning to his team of scientists and technicians. "Prepare her for the final phase. It's time to test our little bird's wings."

____

"You okay?"

Bucky looked up, his eyes snapping away from the laces on his boots as he looked across the Quinjet towards Clint. The man was sharping one of his arrow heads, his eyes occasionally flickering to Steve and Natasha who were in the pilot and co-pilot seats. 

It was the idea covert team - Natasha and Clint had the years of training and experience with HYDRA and its assets, while Bucky and Steve had the insight and strength should there be another super soldier waiting for them. Some of the others had been keen to come along too, but Steve had made the final call as always.

"Yeah," Bucky replied, nodding at the man. They weren't close, but they'd formed an understanding over the last few years. "Just brings up some memories."

Clint nodded, understanding in his eyes. Bucky had been through a lot at the hands of HYDRA, and that would forever haunt him - but Clint knew it wasn't just his time as the Winter Soldier that was resting in his mind right now.

"HYDRA has a way of doing that," he said quietly, testing the sharpness of his arrowhead against his thumb. "But we're not leaving anyone behind this time."

The unspoken name hung heavy in the air between them. No amount of time could pass without the wound still feeling raw. Bucky's metal arm whirred softly as he clenched his fist, pushing down the familiar surge of guilt and anger.

"ETA five minutes," Steve's voice called from the cockpit, breaking the tense silence. "Gear up."

Bucky could see it in the tightness of Steve's shoulders as he piloted, in the way Natasha's knuckles whitened on the controls. It wasn't just him that was thinking about the anniversary of Avery being left behind. No matter how much they told him that it wasn't his or Sam's fault, the guilt and blame would always be there.

"We don't know what we're walking into," Steve's voice carried from the cockpit, all business now. "Intel suggests a possible enhanced individual on site. Approach with caution."

Natasha's voice followed, cool and controlled. "Remember, our primary objective is intel gathering. We need to know what HYDRA's planning, and silently. Last thing we need is a gunfight."

Clint stood, checking his arrowheads one last time as he slotted each one back into his quiver. His eyebrows furrowed as he looked across at Steve who was strapping his shield magnets on to his gloves - something Tony and Isaac had been working on to help his shield always return.

"And if we encounter their new asset?"

Steve turned, his blue eyes meeting Bucky's. There was a flicker of something - pain, determination - before it was masked by the Captain's resolve. 

"We assess the threat and act accordingly. But if there's any sign of..." he hesitated, his eyes flickering to Bucky, "...of prisoners or test subjects, extraction is priority one."

The Quinjet began its descent, the team falling into a focused silence. As they neared the drop zone, Bucky couldn't shake the feeling that something was different about this mission. A chill ran down his spine, a premonition he couldn't quite place.

They touched down silently in a small clearing, the cloaking technology of the Quinjet rendering it invisible to prying eyes. As the ramp lowered, the team moved out with practiced precision, each member falling into their designated role.

Natasha took point, her keen eyes scanning for any signs of security measures or patrols. Clint followed close behind, an arrow nocked and ready. Steve and Bucky brought up the rear, watchful and tense.

The HYDRA facility loomed before them, a stark concrete monstrosity rising from the dense forest. Natasha's voice crackled softly in their comms.

"Two guards at the main entrance. Another pair patrolling the perimeter." 

"I've got eyes on the roof," Clint murmured. "Looks like a sniper nest up there."

Steve's jaw tightened. "Nat, can you and Clint take care of the perimeter? Bucky and I will handle the entrance."

Affirmative responses came through the comms as the team split up. Bucky felt the familiar rush of adrenaline as he and Steve crept towards the main gates. Despite the years that had passed, despite everything that had changed, this felt achingly familiar – the two of them, side by side, ready to take on HYDRA.

They waited in tense silence as Natasha and Clint neutralized the patrolling guards. Then, with a nod to each other, they sprung into action. Steve's shield flew true, knocking out one guard while Bucky's cybernetic arm made short work of the other. In less than two minutes, all four Avengers were inside and successfully still undetected by the rest of the HYDRA base.

As the door slid open with a soft hiss, a chill ran down Bucky's spine. Something felt off, but he couldn't put his finger on it. He shared a concerned look with Steve, who seemed to sense the unease as well.

"Stay alert," Clint murmured as they entered the facility. "This feels too easy."

The team moved through sterile corridors, the fluorescent lights casting harsh shadows. The absence of personnel was unsettling, each empty room they passed increasing the tension.

Suddenly, Natasha froze, her hand flying to her ear as she lifted the comm unit to give herself a little bit extra hearing power.

"Do you hear that?" she whispered.

They reached a heavy steel door, the words "SUBJECT 0-7-3-K" stencilled across it in bold letters. Steve met Bucky's eyes, a silent question passing between them. Bucky nodded, readying his weapon as Clint prepared to breach the door.

The door swung open with a hiss of hydraulics, revealing a cavernous room filled with banks of computers and medical equipment, the heart monitor that Natasha had identified to them all now sounding louder and more prominent.

As the team entered the room, their eyes were immediately drawn to the center, where a figure lay strapped to an operating table. Monitors beeped steadily, displaying vital signs and neural patterns. The person's face was obscured by a tangle of wires and a breathing mask, yet Clint found it hard  to drag his eyes away from them.

Natasha moved swiftly to the nearest computer terminal, her fingers flying over the keys as she began downloading data. Steve approached the table cautiously, his shield at the ready.

"I'm in," Natasha murmured. "But this is... strange. The files are encrypted in a way I've never seen before."

Steve pulled the mask off the figure, his eyes widening in confusion as he looked at the grey skin of the deceased man on the table. He was dead - very clearly, and now that he was up close he realised that the heart monitor wasn't even attached. They were being played.

Clint, positioned near the door, suddenly tensed. "Guys, I don't like this. It feels like—"

A sharp hiss cut him off as a hidden door slid open on the far side of the room. A figure emerged, clad in black combat gear, face obscured by a mask and goggles. The team whirled, weapons raised.

"Stand down!" Steve commanded, shield at the ready. "We don't want to hurt you."

The figure paused, head tilting slightly as if considering the words. Then, in a blur of motion, it launched into action.

Bucky barely had time to register the movement before the attacker was on them. He blocked a vicious kick aimed at his head, metal arm whirring as he countered. But the assailant was fast - impossibly fast, even for his standards - twisting away from his grasp and engaging him in a flurry of strikes.

Steve's shield whistled through the air, but the figure ducked beneath it, rolling and coming up with a pair of wickedly sharp knives. Clint loosed an arrow, only to have it plucked out of the air and flung back at him with deadly accuracy.

As they fought, Bucky felt a growing sense of unease. There was something familiar about the way this person moved, something that tugged at the edges of his memory. He pressed forward, trying to get a better look at their face.

In that moment of distraction, the attacker struck. A knife slashed across Bucky's chest, cutting through his tactical gear. He stumbled back into Natasha, more surprised than hurt, and the figure pressed their advantage and kicked his chest, causing the two to stumble backwards on to the ground.

As Bucky and Natasha hit the ground, the attacker spun to face Steve and Clint. Steve hurled his shield again, but the figure leapt impossibly high, somersaulting over it. In mid-air, they fired a grappling hook that latched onto a ceiling beam, swinging towards Clint with lethal grace.

Clint loosed three arrows in rapid succession, but the attacker twisted in the air, avoiding two and catching the third. They landed behind him, sweeping his legs out from under him before he could react.

Steve caught his returning shield just as the figure charged him. He braced for impact, but at the last second, they vaulted over him, using his shoulders as a springboard. Steve whirled, barely blocking a kick aimed at his head.

"Stop!" he shouted, desperation creeping into his voice. "We're not your enemy!"

The attacker paused, head cocking to the side as if confused. For a moment, Steve thought he'd gotten through to them. Then, faster than he could track, they closed the distance between them. A series of rapid strikes left him reeling, ending with a powerful kick that sent him crashing into a bank of computers.

Bucky struggled to his feet, wincing at the gash across his chest. He watched in horror as the attacker methodically took down his teammates. Their fighting style was unlike anything he'd ever seen... yet, so starkly familiar at the same time.

The attacker seized the moment, leaping overNatasha's prone form towards the computer terminal. With lightning speed, they yanked out the drive Natasha had been using to download files.

"Fuck!" Natasha shouted, scrambling to her feet.

But the figure was already retreating, backing towards the hidden door they'd emerged from. Steve hurled his shield, but the attacker ducked, the vibranium disc clanging off the wall behind them.

In that split second, Bucky locked eyes with their assailant. Even through the tinted goggles, he felt a jolt of recognition.

And then they were gone.

The hidden door slid shut with a resounding clang, leaving the team stunned and battered in its wake. For a moment, the only sounds were their ragged breathing and the hum of damaged electronics.

"Damn it!" Natasha hissed, her fingers flying over the keyboard of the nearest intact terminal. "They wiped everything. We've got nothing."

"Everyone okay?" Steve groaned, pushing himself up from the wreckage of the computer bank.

Before anyone could respond, a piercing alarm cut through the air. Red warning lights began to flash, bathing the room in an eerie crimson glow.

"Self-destruct sequence initiated," a emotionless voice announced over the facility's speakers. "All personnel evacuate immediately. Detonation in five minutes."

"Damn it," Clint muttered, notching an arrow as he scanned for any sign of their mysterious attacker. "We need to move. Now."

As they ran, Bucky couldn't shake the image of their attacker's eyes behind those tinted goggles. There had been something there, a flicker of... what? Recognition? Confusion? Or was he just seeing what he desperately wanted to see?

The cut across his chest stung, but it was nothing compared to the ache in his heart. That fighting style, the impossible speed and agility... it couldn't be. Could it?

The facility was coming apart around them. Chunks of concrete rained down from the ceiling, and the acrid smell of smoke filled the air. They rounded a corner to find their path blocked by a wall of flames.

"This way!" Steve shouted, leading them down an alternative route.

They burst out of the building just as the first explosions rocked its foundation. The team sprinted across the clearing, the heat of the inferno at their backs. Bucky glanced over his shoulder, watching as the HYDRA base collapsed in on itself in a spectacular fireball.

"Everyone on board, now!" Natasha yelled as the Quinjet's ramp lowered.

They piled in, Steve taking the controls and lifting off just as a secondary explosion sent debris flying in all directions. As they soared away from the destruction, an uneasy silence settled over the team.

Bucky slumped into a seat, his mind whirling. He wanted to voice his suspicions, to tell the others what he thought he'd seen. But the words caught in his throat. What if he was wrong? What if it was just wishful thinking, the desperate hope of a man who'd never forgiven himself for leaving her behind?

"Buck?" Steve's voice cut through his thoughts. "You alright?"

Bucky looked up, meeting his friend's concerned gaze. He opened his mouth, then closed it again, shaking his head.

"Just a scratch," he muttered, gesturing to the gash on his chest.

His chest was fine, but his mind... either he was right or his mind was starting to play tricks on him again. If he was right, the implications that came with that... Bucky wasn't sure what was worse.

____

"You didn't kill them."

Osprey stood still as Dr Faust circled her, a snarl on his lips as he clenched his fists at his side. She didn't meet his eyes, instead staring straight ahead at a screw on the edge of a metal panel in front of her. She had failed her mission - and punishment was due.

"Why didn't you kill them?"

She didn't reply.

"Subject 0-7-3-K, repeat your orders," he ordered, his voice colder and quieter now. She ignored the way that some of the other Hydra agents in the room shuffled uncomfortably at the change in his voice. "Now."

"Lure them in, recover any data and terminate the threats."

"And yet, here we are. The Avengers escaped, and you..." He paused, studying her impassive face. "You hesitated."

Osprey remained silent, her gaze fixed on that distant screw. She couldn't explain the strange sensation that had overcome her during the fight, the way her body had seemed to move of its own accord, parrying moves she couldn't remember ever having fighting against. 

"Look at me when I'm speaking to you, Osprey," Faust snapped, grabbing her chin and forcing her to meet his gaze. "What happened in there? What made you disobey your programming?"

For a moment, something flickered in Osprey's eyes – confusion, perhaps, or the barest hint of defiance. But it was gone as quickly as it appeared, replaced by the vacant stare of a well-trained soldier.

"I... I don't know, sir," she replied, her voice devoid of emotion. "It won't happen again."

Faust released her chin, taking a step back. His cold eyes scanned her face, searching for any sign of deceit or hidden emotion. Finding none, he nodded slowly.

"No, it won't," he agreed, his voice dangerously soft. "Because we're going to make sure of that." He turned to one of the nearby technicians. "Prepare the chair. It's time we reinforced our little bird's conditioning."

As the technicians scurried to obey, Faust leaned in close to Osprey, his breath hot against her ear. 

"You're right about one thing, my dear. It won't happen again. Because next time, you won't just fight the Avengers – you'll destroy them. And you'll do it without a second thought."

Osprey didn't flinch as she was led to the chair, her steps measured and calm. As the restraints closed around her arms and the neural interface lowered towards her head, she closed her eyes. In the darkness behind her eyelids, she saw a flash of green eyes and red hair, filled with recognition and something else she couldn't name. 

Then the pain began, and all thoughts were washed away in a tide of agony and blinding light.

_____

"Hey Barnes," Isaac murmured as Bucky walked into his technician room, not a stranger to the once-Winter Soldier walking in and requesting small tweaks on his arm after a mission. 

It had been something that had taken them a while to see eye to eye on, but eventually Bucky had agreed that small checks on the hardware were helpful.

Bucky was silent as he entered, his face a mask of barely concealed tension. Isaac's eyes flicked to the tear in Bucky's tactical gear, noting the angry red gash beneath.

"Rough mission?" Isaac asked, gesturing for Bucky to take a seat.

Bucky nodded, his jaw tight. The tension between them was palpable, a reminder of the unspoken blame that still lingered. He sat down heavily in the chair next to Isaac's workbench, extending his metal arm without a word.

Isaac nodded, reaching for his tools. As he began running diagnostics on the arm, he couldn't help but notice the faraway look in Bucky's eyes, the tightness in his jaw.

"You know," Isaac said carefully, "if something's bothering you, you can talk about it. I may not be a therapist, but I've got two good ears."

"Nothing to talk about," Bucky replied gruffly. "Just doing my job."

Isaac worked in silence for a few moments, the only sound the soft whirring of Bucky's arm as he ran tests. Finally, he spoke again, his voice low and measured.

"Look, Barnes, I know we've had our... differences. Especially when it comes to Avery." He paused, noting how Bucky tensed at the mention of her name. "But I cared about her too. If there's anything—"

"You don't get to say her name," Bucky interrupted, his voice cold. "You don't get to pretend you care, not after what you did."

Isaac set down his tools, meeting Bucky's glare. "I've made mistakes, I know that. But Avery was—is—my sister. Whatever you think of me, don't ever doubt that I miss her even more than you do."

For a long moment, the two men stared at each other, years of unspoken tension hanging between them. Then, almost imperceptibly, Bucky's shoulders sagged.

"We encountered an enhanced individual," Bucky said finally, his voice low. "Someone new. Someone..." he trailed off, uncertain how to voice the suspicion that had been gnawing at him since they'd returned.

Isaac's hands stilled for a moment before resuming his work.

"Someone familiar?" he asked quietly, not meeting Bucky's eyes.

"I don't know," he admitted. "Maybe I'm seeing things. Wishful thinking." He let out a bitter laugh. "Or maybe I'm just going crazy."

Isaac's brow furrowed as he made a minor adjustment to Bucky's arm. 

"That must have been unsettling," he said carefully, his voice neutral.

"Yeah," Bucky murmured, his eyes distant. "It was like seeing a ghost."

"You know," Isaac said after a while, breaking the silence, "sometimes our minds play tricks on us. Especially in high-stress situations. The brain has a way of filling in gaps, making connections that might not be there."

Bucky nodded slowly, grateful for the rational explanation. Isaac's hands stilled for a moment once more, a flicker of emotion crossing his face before he resumed his work

The two men lapsed into silence again, each lost in their own thoughts. Bucky watched as Isaac meticulously checked each component of his arm, making minute adjustments here and there. The familiar routine was oddly comforting, a small island of normalcy in the sea of uncertainty that seemed to be swallowing him whole.

"All done," Isaac announced finally, setting down his tools. "Everything looks good, but let me know if you notice any issues."

Bucky flexed his metal fingers, testing the arm's range of motion.

"Thanks," he said, standing up. He hesitated for a moment, then added, "And thanks for... you know. Listening."

As Bucky walked away, Isaac watched him go, a troubled expression on his face. He turned back to his workbench, his eyes falling on a framed photo hidden behind a stack of schematics. 

In it, a younger version of himself smiled alongside a woman with vibrant eyes and a mischievous grin. Isaac picked up the photo, his thumb tracing the outline of his sister's face.

"I miss you."