Disclaimer - I do not own anything associated with the Marvel Cinematic Universe or Harry Potter.

November 1943, Austria

Steve carefully manoeuvred through the weapons factory, braced to fight an enemy at any moment. So far, everything had gone to plan: he'd landed safely after jumping out of the aeroplane, successfully located HYDRA's factory, and managed to sneak on board a cargo truck just before it entered the facility. He'd had to knock out a few soldiers on his way in but he didn't exactly have a problem with that if he wanted to succeed in his goal of rescuing his best friend, Bucky Barnes.

He rounded another corner and found himself suddenly blasted off his feet. Anybody without his super-soldier body would've been knocked out cold by the collision with the wall but Steve was merely winded. He prepared himself for some sort of warning siren due to his being discovered but there was no sound. Stranger still, he stared in confusion at the spot where the blow had come from because, as far as he could tell, there was nothing there that could have attacked him.

He blinked to clear his hazy vision and realised that he could see… something? There was a part of the dark corridor that didn't look the same as the rest. His mind puzzled over what sort of technological contraption it could be to throw him forcefully into the air but then he saw it move. Alarmed, he launched himself at it and it was only as he knocked it to the ground that he realised that it was a person. Amazed as he was, Steve wasn't about to take any chances and raised his fist to knock the invisible person out, but their voice cut him off.

"No!"

It was a female voice – with a British accent if he wasn't mistaken – and he stared down at the impressively camouflaged figure in astonishment.

"You need to get under cover," she warned him lowly and his brain was just able to function enough to realise that she was correct because somebody could walk by at any moment and he wasn't currently hard to miss. He kept a firm grasp of what he assumed was her wrist and pulled them into a shadowy recess.

"Who are you?" he whispered.

"Who are you?" she countered.

"I asked first," he pointed out.

"Well, I'm not HYDRA," was apparently the only answer she was willing to give as she unsuccessfully attempted to jerk her arm from his grip.

"Neither am I," he replied.

"Yes, your extremely patriotic shield makes that somewhat obvious," she muttered. "Where did you even get that?"

"Look," he said, his patience beginning to wear thin, "my best friend is being held here – I've got to rescue him. Bucky's all I've got."

There was a pause from the concealed woman. "I suggest we join forces, then; a rescue operation is my reason for being here too."

Steve considered her offer. He didn't want to put her in danger but, apparently, she seemed to be perfectly happy doing that of her own accord. Nor did he feel particularly comfortable with her believing him to be experienced in dangerous missions such as these. However, the odds were so stacked against him that he was willing to accept any help that he was offered.

"Agreed," he said, then frowned, "But I can't help thinking that I would be less likely to accidentally injure you if I could see you."

Her pause was longer this time. "All right," she allowed eventually, "But if things go wrong or we encounter other people, don't expect to see me anymore."

Steve supposed this was reasonable enough; if he was capable of such impressive camouflage, he'd use it at every opportunity too. He watched in amazement as the woman in front of him slowly reappeared in front of his eyes. "How do – "

"I can't tell you," she interrupted, correctly assuming he wanted to know how the transformation was possible. "I can't tell you anything."

Despite the gloom, he could see her quite clearly now. She was shorter than he'd expected – even with the extra few inches that her curls added to her height. Her delicate features fit well with her petite frame and her dark brown orbs looked up at him challengingly, as though daring him to make some comment about her unsuitability to carry out her objective.

When no such words fell from his lips, she told him, "I think the prisoners are being held down here." She pointed to a corridor that branched off the one they were currently in and he nodded.

"I'll go first," he said, noticing that she didn't appear to be armed with a single weapon or means of defending herself. He checked that the way was clear and then moved through the shadows in the direction she had indicated.

She was right. The corridor led to a large room where men were being held in cages. Four armed guards were patrolling on a platform above the prisoners.

"I'm going to disappear," she whispered to him, doing so in front of his eyes. "You take the closest guard, I'll take care of the other three." He was about to object the likelihood of that plan succeeding but he felt her brush past him and he realised the decision wasn't up for discussion. The guard nearest him showed no indication of being aware of either his or the woman's presence so he crept forwards and used his shield to knock the man unconscious. He grabbed the guard to stop him falling noisily to the metal below their feet and disturbing the other guards, but when he looked over to check on her progress, he saw that all three of her guards were slumped on the metal without a sound being made.

A bunch of keys landed at his feet, making a loud clang, which attracted the attention of the prisoners below him.

"Who're you supposed to be?" one of them asked as they peered up at him.

"I'm…" Steve looked down at himself and reasoned there was only really one answer to give, "Captain America."

He grabbed the keys and jumped down to the cells below, ignoring the confused reply of, "I beg your pardon?" from one of the other soldiers. He moved quickly from cell to cell, looking for any sign of Bucky, but he couldn't see him anywhere.

"Is there anybody else?" he asked the liberated men around him, "I'm looking for a Sergeant James Barnes."

"There's an isolation ward in the factory," one of the soldiers replied, "but no one's ever come back from it."

"All right," Steve said, trying not to lose hope of finding Bucky alive. "The tree line is northwest, eighty yards past the gate," he told them. "Get out fast and give 'em hell. I'll meet you guys in the clearing with anybody else I can find."

"Wait. You know what you're doing?" the soldier asked in disbelief.

"Yeah," he replied, trying to project a confidence he didn't quite feel. "I've knocked out Adolf Hitler over two hundred times." He ran off to continue the search for Bucky but soon heard the tell-tale chatter of gunfire and booms of explosions, soon followed by the anticipated alarm as the prisoners made the most of their escape.

Moving through the facility was much more difficult now but none of HYDRA's soldier proved too difficult to overcome as Steve kicked, punched and swiped his way through them. A couple of times, he came across a soldier that had already been knocked out and he heavily suspected that his mysterious, invisible ally was responsible.

He emerged onto a railing, overlooking the main factory floor. A loud, piercing whistle caught his attention and he looked to locate its source. He couldn't be sure but it seemed to have come from a corridor to his left. He could be wrong about the identity of the person who'd made the signal but he expected HYDRA would just shoot him outright rather than try to lure him down a dark corridor. As Steve turned into the passage, he saw a figure emerge from a room and both men momentarily paused at the sight of each other. The other man took a few nervous steps backwards and then fled out of sight. Steve ran a few steps after him but was distracted by a groaning voice coming from one of the rooms off the corridor. He cautiously stepped inside, and saw that the room was set up for some sort of medical procedure. A murmuring man was strapped to a table and Steve realised, with a mixture of relief and anger, who it was.

"Bucky?" he asked, trying to get the dazed man to focus. "Oh my God," he muttered, angrily pulling the straps off his body.

"Is, is that…?" Bucky asked weakly.

"It's me," he confirmed, "It's Steve."

"Steve," Bucky repeated slowly.

"Come on," Steve said, pulling his friend upwards.

"Steve," Bucky said with much greater lucidity and a small smile as he stumbled to his feet.

"I thought you were dead," Steve muttered as Bucky stared at him confusedly.

"I thought you were smaller," he countered before Steve half supported-half dragged him from the room. "What happened to you?"

"I joined the army," he replied simply, before giving a little more detail about the procedure Dr Erskine's had put him through.

"Did it hurt?" Buck asked, attempting to walk on his own.

"A little."

"Is it permanent?"

"So far."

A huge series of explosions began as they came back above the factory floor and Steve urgently suggested they climb higher.

"Captain America!" a voice called across to him. "How exciting!" Steve looked over at the man on the other side of the warehouse, noting the thick accent and the red YHDRA symbol emblazoned on his black coat. He also saw that the small man he'd seen in the corridor earlier was standing behind him. "I am a great fan of your films!" A platform stretched between them and the man walked towards it with Steve doing likewise. "So, Dr Erskine managed it after all. Not exactly an improvement but, still… impressive," he commented lightly, and Steve realised that this must be Johann Schmidt, the head of HYDRA and the first recipient of Erskine's serum.

Anger swelled within him and he forcefully punched Schmidt in the jaw, making him stumble backwards. "You got no idea," he claimed.

"Haven't I?" Schmidt questioned challengingly. He launched his own punch and Steve quickly raised his shield in defence. To Steve's surprise, an imprint of Schmidt's fist was left in the metal. Steve reached for his gun but Schmidt was too quick, knocking him backwards and making the gun fall from his grasp. Schmidt advanced on him but Steve kicked him away strongly. The two halves of the platform suddenly started to retract and Steve watched as his enemy slid away from him. "No matter what lies Erskine told you," Schmidt called, "you see, I was his greatest success!"

Schmidt grabbed at his own neck and Steve and Bucky watched with a faint feeling of horror, as he pulled the skin off his face to reveal a shining, red skull in its place.

"You don't have one of those, do you?" Bucky asked, slightly disturbed.

"You are deluded, Captain," Schmidt called to him, "You pretend to be a simple soldier, but in reality, you are just afraid to admit that we have left humanity behind!" he claimed, tossing his mask into the fiery inferno below them, before making his way to an elevator set back in the wall. "Unlike you, I embrace it proudly! Without fear!"

"Then how come you're running?" Steve yelled as the door slid shut.

A further set of explosions erupted below them, forcing Steve and Bucky to climb even higher. There was a door they could escape through on the opposite wall so all they had to do was walk over an iron girder without falling fifty feet to a living hell below them.

"Let's go. One at a time," Steve said helping Bucky climb over the railing and onto the metal beam below. Anxiously, he watched Bucky inch across the metal but he saw that it was starting to crumple. It gave a shudder, and Steve was convinced that Bucky's loss of balance would see him fall, but he somehow managed to stay on. Bucky took the last few steps quickly, just as the beam looked like it was about to give way.

"Come on!" Bucky yelled, gesturing to him eagerly. Steve looked at the girder sceptically, not convinced that it would take his weight.

"Go," a recently familiar voice urged next to him. He turned his head, forgetting that he wasn't likely to see her. "It'll hold, I promise."

"Steve, let's go!" Bucky cried.

Understandably, Steve put his foot on the beam with great caution, gradually transferring his weight until he was fully standing on it. He hurried across it quickly because his brain seemed to be showing him that the beam was attached to nothing – it was hovering barely an inch below where it should be joined to the rest of the structure! Bucky clapped him enthusiastically on the back as he made it to the other side, and hurried for the door, but Steve lingered to look back at where he'd left the woman. Had she followed him across?

"Thank you," he said, unsure whether she'd hear him.

"You don't need to thank me," she replied, her voice just distinguishable over the booms below them. "You won't even remember me. Obliviate."

A/N Thank you for reading!