Mutant

by Liliththestormgoddess

Summary: It's been three months since the Avengers last saw one another after saving the world from the Chitauri. Now, they're called in to deal with a mad scientist who is obsessed with rabid mutants. It seems like a simple operation, but it's only later when they realize something horrible has happened to Clint.

Rating: T for violence, some mild swearing.

A/N: Finally, the multi-chap fic I have been working on. This took much longer than I expected. When I hit a wall with this, I actually wrote another multi-chap fic. At the end of this story, I might post a preview.

So, this story is complete. I will try and post once or twice a week, depending. Please read, review, and enjoy!

Disclaimer: I don't own the Avengers.

Chapter 1 - Flight

"These things are god-damn ugly," Clint grunted, aiming and loosing an arrow straight into the neck of some tiger-fish-lizard…thing. It let out a spine-chilling shriek and keeled over. Captain America leapt out of the way of its falling body, pausing only long enough to nod to the archer in thanks before turning his attention to the next approaching mutant. His shield was a blur as he slung it around, driving it into the ribs of the mutant, giving Natasha a chance to leap on it and cut its throat.

She leapt back off, not even blinking at the green blood that covered her hands and her suit. "They smell like shit, too," she quipped.

A giant roar sounded from behind them, and the Hulk swept through, swinging his fists through several mutants. His cries grew louder and angrier when one sank it's teeth into his arm, and he spent several seconds swinging it around, attempting to dislodge it.

Lightening and thunder crackled and rained down from the sky, directed by Thor. He was vaporizing most of the mutants he saw; some, however, were irritatingly immune. In fact, if his eyes were to be believed, they were swallowing the lightening.

One such mutant – one with a lion head and a fish tail – breathed fire directly into the path of the oncoming Iron Man, who was pushed back a few feet and dipped slightly in the air. Tony scowled behind his mask as JARVIS calmly told him the damage the fire had done – minimal, as his suit was obviously flame retardant – but enough to piss him off. "Not cool, fish lips," he said, and struck him with a blast from one of his hand repulsors. The lion-fish let out a piercing wail and erupted into flames. When the fire cleared, there was nothing left of it.

Atop his rooftop perch, Hawkeye calmly watched everything and everyone. He kept tabs on where his team was at all times and where the mutants were and how many were left. He continued to shoot down the mutants, but movement to his left caught his eye. The rooftop door on the building next to him slammed open and men streamed out, toting large semi-automatic guns. They spotted him immediately, and Clint tucked and rolled, feeling the gravel bite into his face as the bullets dove into the ground around him.

"Alright, who called in reinforcements?" he cracked as he made a mad dash to the ledge of the roof. He didn't slow down as he neared it, instead springing off the edge. The next roof was slightly higher than the one he had just left, but he called on his old acrobat training and grasped the ledge with both hands and used all his upper body strength to swing the lower half of his body up and onto the roof.

He continued the roll, avoiding the bullets and ignoring the angry shouts of the men behind him. He heard metal crash against metal, and spared a glance behind him to see that grappling hooks were being put to use.

"Hawkeye, what's going on?" Rogers demanded in his ear.

"Nest compromised. I'm taking the stairs." There were only two buildings in the middle of the jungle where the mad scientist had set up shop, and Clint had reached his end point. Wrenching open the door of the roof in front of him, he dashed down into the building.

He stopped inside the wide, dark room, and eyed the lab apprehensively. Shelves and shelves were lined with bottles and bottles of blood. He assumed it was all the mutant's blood that the scientist was using. SHIELD would want to seize and study it, he knew. But for now, he wanted nothing to do with it.

He could hear the men getting closer, so he began to run towards the exit. He was nearly there when his feet caught something and he stumbled slightly. Glancing down, he saw the trailing end of a thin silvery string. His eyes grew wide. "Shit," he swore, and desperately leapt for the door. He'd barely cracked it open when there was a deafening explosion from behind him, pain and heat enveloped his body, and everything went mercifully black.

The nearby Avengers turned as the building in front of them exploded. They saw Hawkeye's form sail out through the door and tumble heavily to the ground. He landed in a heap, unmoving.

Thor obliterated the last mutant as Natasha and Steve scrambled over to their fallen comrade.

Clint was unconscious, with a nasty cut on his forehead that bled down the side of his face. His uniform was covered in debris and shredded and singed in several places.

"Barton!" Natasha barked, kneeling next to him. When she got no response, she tapped his cheek none too gently. "Clint!"

She got the desired response. He moaned and tried to move away from her touch. Then he coughed harshly and opened his eyes, taking in the faces hovering over him, the burning building behind them, and the fact that every inch of his body hurt. "Ow," he said.

Natasha smirked. He began to peel himself off the ground, slowly rising to his feet, but that proved to be too fast. He swayed, but the Cap's hand grabbed his bicep, steadying him. When his head stopped spinning, he nodded and Steve let go.

He squinted around them, wiping the blood from his eyes. "We get them?" he asked. His voice sounded horrible, and he coughed once more, trying to get all the dust from it.

Stark dropped down next to them, and Thor ambled over to join them. "Not another living thing left," Stark said, the mask of his suit sliding up. "Not even the hired help." He looked pointedly at Barton.

"Hey," he said defensively. "What kind of idiot puts a trip wire in a laboratory?" He tried to joke but ended up in another coughing fit. When he finished, he scowled. "Jesus."

"You're lucky to be alive," Rogers pointed out, his face betraying his concern. "I really don't know how you survived that blast."

"It's kinda hard to kill me, Cap." Barton smirked, then turned serious. "I think the explosives were set up more in the back of the lab. Closer to the security. Probably nothing left of them." He turned to look back at the smouldering lab, wincing. "SHIELD wanted all that crap in there. Damn."

The five of them stood there waiting for their evacuation and clean-up team while the Hulk lumbered around, growling at the mutant remains.

"I'm fine!" Barton snapped angrily.

Natasha, eyes ablaze, put her hands on her hips. "You damn well are not fine," she spat. Her eyes roamed over his body, cataloguing his obvious injuries. She knew there was more that she couldn't see. The man had survived a bomb, for Christ's sake.

"I'm not going to medical," he growled as he stowed his gear away in his locker. "I don't need it."

Natasha pursed her lips, weighing her options. Neither of them really liked medical aboard the helicarrier, but he really needed medical attention. They were more of field medics, and she could only do so much. She offered up a compromise. "Fine. But we're heading with the others to Stark tower and you let Dr. Banner patch you up." While his specialty was not a medical doctor, he certainly knew more than either of them.

He regarded her for several long seconds before nodding tersely. "Fine."

While Banner had settled down at Stark tower after the first battle, the rest of the tower remained vacant save for Tony, and Pepper when she wasn't elsewhere doing business. Steve had traveled a bit, Thor had gone back to Asgard and only returned to visit Jane Foster two days before the mutant science experiment crisis, and Clint and Natasha had been busy with various other missions for SHIELD. So it was the first time all of them had been together in the same room, and not having to save the world.

Pepper had come running towards the opening elevator doors when they arrived. Her eyes held the fear and apprehension that she had felt ever since Tony had left. She immediately grabbed him and began searching for any injuries, even when Tony grabbed her hands and assured her he was fine.

Her eyes fell upon the rest of the rag-tag group that stumbled out of the elevator and looked uneasily around the room. "Tony…?" she asked, eyeing the group. The only one she recognized was the solitary female figure, Natalie – Natasha, she corrected herself.

"Ah, come, meet the gang," he said grandly, sweeping an arm out to the others. "Well, you've met Bruce and Mrs. Deadly. This here is Steve Rogers, the genuine Capsicle and America's golden boy; Thor, who comes from another planet via a rainbow bridge of all things; and Clint Barton, who has an identity crisis and thinks he's Robin Hood. Guys, this is the most wonderful woman in the world: Pepper Potts."

"Lady Potts, it is a great pleasure," Thor rumbled as he took Pepper's hand and brought it to his lips. He gazed at her and smiled charmingly; completely missing the glare Tony sent his way. When Thor let go of her hand, Tony pulled her towards him possessively.

Pepper blushed after the dramatic introduction, but smiled at the group. "Um, thank you. Would you like anything? Something to drink?"

Steve spoke up. "A water please, ma'am," he said politely. Stark just rolled his eyes. Pepper dashed off to the kitchen as the Avengers moved towards the sitting room.

Clint walked stiffly beside Natasha, who was shooting him death glares. There wasn't much in the world that Hawkeye feared; but the Black Widow was certainly one of them.

He sighed and moved up behind Dr. Banner, who had lingered at the edge of the room, not joining the others in sitting on the couches drinking the water Pepper had retrieved. "Dr. Banner?" he asked softly.

Banner jumped a little, having not heard the spy sneak up behind him. He turned to look at the battered Clint, and already guessed what was coming. "Agent Barton?"

Barton's eyes darted anxiously, and Banner followed his gaze towards the irate Russian sitting on the couch shooting him death glares. He fought off the smirk pulling at his lips. Finally, Clint said in a low voice, "I was hoping you could help me."

Bruce nodded. "Sure, of course. Here, let's go down the hall." The two walked from the room unnoticed, and slipped into an empty room a few doors down. Clint sat on the bed while Bruce retrieved the necessary medical supplies. When he came back, he said, "You know I'm not a medical doctor – "

Clint cut him off. "I know. It's fine. Just do what you can."

Bruce let out a heavy breath and nodded. "Don't like the doctors on base?" he asked. He got a guarded stare in return. "Okay," he finally said. "I'll start with the head wound."

After cleaning and patching up the cut on his head – Bruce determined that Clint did not receive a concussion – Bruce had Clint remove his shirt so he could get a look at his upper body. His chest seemed to be fine, and there were only minor cuts and burns on his arms. His back, however, seemed to have taken the brunt of the blast. Numerous small debris was lodged in his back and Bruce painstakingly pulled each one out. Clint never said a word or made a sound, and Bruce tried to ignore the numerous other scars that littered Clint's body; some old, some newer, and some that looked extremely painful.

When he was done he stood up and discarded the bloody clothes in the trash. "I'm sure there's some painkiller around – " he began, but again, Clint cut him off.

"Don't need it. Thanks Doc," he said and left.

Bruce watched him go, sighed, and went back to the sitting room where the rest of them – minus Clint – sat.

Clint wouldn't admit it to anyone, but his head was spinning. The walls kept looming over him and he constantly tripped over the rising floor. He made his way to the closest room, shut and locked the door behind him, and fell onto the bed. He was still half clothed in his tattered uniform, but he didn't care. There was an insistent ringing in his ears that refused to abate, and his head pounded like someone had smashed it around a few times. He shut his eyes tight and fell into sleep.

When he awoke, he was surprised to see the sun streaming in the window. Blinking blearily, he tried to determine where he was and what time it was. His brain felt extremely sluggish.

"Good morning, Agent Barton," a posh British voice greeted him, and Clint whipped his head around, unsheathing the knife strapped to his thigh. "I am JARVIS, Mr. Stark's artificial intelligence system."

Dropping the knife, Clint unclenched his hands and groaned, dropping his pounding head back into the pillow. At least that answered one of his questions. He was at Stark tower. He vaguely remembered that. "What –" he broke off into another coughing fit that had him curling up into a ball. When he finally caught his breath again, he asked, "What time is it?"

"10:13 am," the voice responded.

"Damn," Clint groaned, pushing himself off the bed. Everything twisted around him, and he stumbled to the ground. Did he get drunk last night? He couldn't remember. He hadn't felt this shitty in a long time.

"Should I get assistance, Agent Barton?" the AI asked.

"No," Clint groaned. "I'm fine." He managed to get his legs under him and he stood and stayed there. It felt like a huge accomplishment. He rotated his sore shoulders and neck, feeling the muscles groan and protest. Was he coming down with something nasty? He slipped a shirt that he found in the closet over his head and winced as it rubbed against all of his new wounds.

"I need coffee," he muttered. That would solve all his problems. He stumbled towards the door, hearing JARVIS inform him, "the kitchen is located down the hall and on you're right." He waved a hand lazily and set off to find the kitchen.

He found it easily enough and stumbled in, expecting it to be empty. Instead, Pepper Potts sat at the table, drinking coffee and making notes in a file. She looked up at the new arrival, and her eyes grew wide. Clint figured he must be a sight to look at. But he really didn't care at the moment. All he cared about was coffee.

"Uh, Miss Potts," he greeted as politely as he could.

"Good morning, Agent Barton," she returned, shocked eyes still fixed on him. He was glad that he had remembered to put on a shirt, because he really didn't want her staring at his back. Her eyes finally pulled away and she glanced over at the half empty coffee pot. "Coffee?" she asked.

"Yes," he said and dashed towards it. He was filling up a cup and skipping sugar and milk and just going straight for black because he was too impatient, when Bruce walked into the kitchen.

He looked slightly taken aback by Clint standing there, and Clint began wishing he'd actually taken the time to look in the mirror before he'd left his room. Did he really look as bad as he felt?

Bruce offered up a smile. "How are you feeling? Did you sleep well?" he asked as he emptied out the coffee pot.

"Fine," was all Clint offered. He was focusing on not throwing up. There was a rushing sense of vertigo and the lights were stabbing at his eyes. He slumped into the nearest chair at the table, at an angle from Pepper. Bruce remained at the counter, frowning at him over his cup.

"Clint?"

He didn't hear Natasha come in. He hunched over his mug, trying to find a position that didn't bring upon extreme agony. It was getting hard. There was a sharp pain in his abdomen, and his back muscles felt like they were being stretched. He felt his hands begin to shake, but he wrapped them tighter around his mug, trying to quell it. He succeeded in spilling most of the hot liquid on his hands. He didn't even feel it.

He was suddenly very cold, and he broke out into shivers. He heard loud voices, but he couldn't see them. His vision was swimming in and out, the colours blending together until nothing was recognizable.

Suddenly, he felt the sensation of falling. Was he on the floor now? It didn't matter. He curled inwards, trying to stop the stabbing in his abdomen. He shut his eyes tight. He began to cough again; this time it was wet and sticky and something was on his hands. It looked red. He couldn't stop coughing. It shook his whole body. He felt his heart beat faster and faster and faster…and slam to a stop.