DISCLAIMER: I don't own Chicago Fire, or any of the characters. I'm just borrowing them to avoid my real life. Thanks Dick Wolf, you're quite a dude.

A/N: Okay, so I've just recently become obsessed with this show, which naturally means I couldn't not post the first story idea that came to mind. Forgive me for grammar/spelling errors and anything that seems out of character or any ridiculous plot points, I really threw this together pretty quick to get it out of my head. Any firefighting techniques or medical tactics are purely fictional (thanks Wikipedia), and if anybody ever searches my internet history they're going to think I'm a psychopath for some of the things I did research for this...

Anyway, I hope you enjoy my first attempt at this fandom. I just love this show and these characters so much, I can't get enough. And a three week break? Are you effing kidding me NBC?

Alright, let's get on with it, shall we?

When life starts to get back to normal, and the daily routine is so routine you can barely remember the tumultuous feelings from past tough times, that's when you should be paying the most attention.

"Second floor partially engulfed," Casey's voice came through Severide's radio as he was finishing up clearing a room on the first floor. Severide's team was clearing one, while Casey and his men had headed up to two to clear the building as fast as possible. The old two-story home seemed unstable, likely abandoned by any real owners years ago and now inhabited by squatters.

"Fire department! Call out!" Severide shouted into the room as he cautiously made his way in. This room wasn't even in flames, as the fire had started in the front rooms and made its way up rather than back where he was. Nobody answered Severide's shout, and as he was about to vacate the room he noticed something unusual on a rickety table on the far side of the room. He cautiously approached what was looking more and more like a chemistry set. His suspicions were confirmed as he stopped in front of the table. He hit the button for his radio.

"Looks like we've got some kinda drug lab here Casey," he yelled through his mask. There was a moment of static before Casey responded.

"More reason to get the hell outta here. Second floor is clear, looks like their chemistry experiment went wrong and our squatters decided to bail before the police showed up."

"Copy that," Severide replied, heading for the door as Capp and Hadley confirmed the rest of the first floor was clear, "let's move out."

Hadley was making his way to Severide from across the landing, gesturing toward the back door exit. Severide lifted a hand in response, but something still felt off about this room and he paused five steps from the door. Just as he was turning to do a quick final sweep, something heavy smashed into Severide from his left, knocking him to the floor. There was a cracking sound, which Severide instantly realized was the plastic of his mask breaking from the sudden and forceful impact with the floor. When his vision cleared, Severide saw a man running for the door, only to be tackled by Hadley a few steps from freedom.

Severide tried to take a few deep breaths to clear his head before trying to right himself, only to realize his breathing unit was no longer working. He ripped the gear off his face and took several deep, smoky breaths. He coughed and realized he needed to get outside if he wanted air to clear his head.

"Lieutenant!" Capp shouted, his voice muffled by his mask as he made his way quickly toward Severide. Capp wrapped Severide's arm around his shoulders and hefted him to his feet, making a beeline for the exit.

Outside, Severide coughed the smoke from his lungs as Capp lowered him to the bumper of Dawson and Shay's ambulance.

"What happened?" Shay yelled at Capp as he unwrapped himself from the Lieutenant.

"Some tweaker was hiding in the closet I guess," Severide managed between coughs. Shay and Capp looked over to where Hadley was manhandling said tweaker into the waiting handcuffs of a CPD officer. "He blindsided me and made a run for it."

"Didn't work out so well for him," Dawson quipped as she started to take Severide's vitals. He brushed her away.

"I'm alright," he said casually, "just a little smoke and maybe a bruise or two." Shay leveled a glare at him. "Seriously Shay, it was like a minute without a mask, I'm fine!"

"Fine," she huffed, after exchanging a look with Dawson. Severide stood from the bumper, noting the trees were a stranger color than normal. He played it cool, not wanting to draw Shay's concern and risk a trip to the hospital.

"Let's pack it up!" Boden shouted as the truck and squad teams were clear of the building, the flames subdued.

Casey strode past the ambulance as Severide made his way back to his truck.

"You all right Kelly?" he asked, a look of concern crossing his face. Severide waved him off.

"Yeah, the only thing that hurts is my pride from letting a tweaker get the drop on me," he laughed. Casey smiled and chuckled, punching him lightly on the shoulder.

"Losing your touch, Lieutenant Severide?" he laughed, climbing into the passenger seat of 81. Severide chuckled, but felt a strange burning anger flare up at Casey's words. He knew Casey was joking. The two of them were finally starting to get back on good terms. For the first time since Darden's death Severide was starting to feel like he and Casey would actually be friends again. He shook his head trying to fight off the unprovoked feeling of anger and made his way to the Squad rig.

Back at the station, the men were piling out of the trucks, dropping their gear and milling around. Cruz and Mouch headed straight for the television to catch up with the baseball game they'd had to run out on. Casey strode over to Severide as he was swapping out of his fire boots.

"Beers after shift?" Casey asked casually, strolling up beside Severide at the Squad truck. Severide looked up to respond and again the world had taken on a strange hue, the trucks that surrounded him seemed foreign, and the picture was blurred at the edges. In the middle was Casey's face, which was slowly shifting from a questioning look to a look of concern.

"Severide?" Casey's words were distorted, like he was under water. His facial expression morphed again, but this time, in Severide's haze, he was laughing. Rage suddenly overwhelmed any other thoughts in Severide's head and he lunged at Casey, catching his jaw with a right hook. Before Casey knew what was happening, Severide had launched a full-on attack. Still reeling from the first hit, Casey was unprepared for the second punch to his face, quickly followed by a hit to his midsection that doubled him over.

"Kelly, stop!" Casey yelled, holding his stomach with one hand and holding the other out in a gesture of surrender, trying to back away.

But Severide was like a man possessed. He continued to launch punches at Casey, more hitting their target than not. He landed blows to Casey's face, eventually knocking him to the ground. Something was clearly wrong with Severide, and Casey initially didn't hit back in case it provoked him further, but he'd waited too long and was now dazed and in so much pain he couldn't have fought back if he wanted to.

The other men heard the commotion and came running.

"Lieutenant!" Hadley shouted, stepping in to catch Severide's arm and halt the attack. Instead, Severide caught his arm, twisted it at a vicious angle and tossed Hadley aside like a rag doll. The other men stepped back in shock, and Herrmann shouted for Shay.

Severide turned his attention back to Casey, as if nothing had happened. He brutally kicked him in the ribs several times. He'd lost control of his brain, rage the only voice in his mind and it was screaming that Matt Casey had to pay. For what, his brain could not recall, only that damage needed to be done.

Casey was losing grip on the world around him when suddenly Severide's hand gripped his hair and yanked his head up. The look in Severide's eyes was one Matt had never seen before: cold, and malicious.

"Kelly, it's me, it's Matt," he gasped, winded from the attack. "Stop Kelly, please," he panted. Severide considered him for a moment. But his brain had lost all touch with reality, with what was real and what was not. He yanked Casey up by his hair and his shirt, ruthlessly slamming him into the side of the Squad truck and wrapping his hands around his neck.

Matt's eyes grew wide and a jolt of terror shot through him. Something had happened to Kelly, he didn't seem to recognize Matt and now he might strangle him to death. Matt stared into the glazed and unfeeling eyes of his friend. He could feel blood running down his face from various cuts and scrapes he had developed in the attack.

"Kelly," he choked out, trying to pry Kelly's hands from his neck, "Kelly stop, plea-" but Severide only tightened his grip on Casey's neck, cutting off his air completely and silencing him. The others were on Severide now, tearing at his arms, trying to loosen his grip on Casey, but it was no use. It was as if Severide's brain had diverted all other functions to one goal: killing Matt Casey.

He was too strong in his blind rage, and even two men on each arm couldn't release the hold on Matt's throat.

Shay and Dawson came running with a jump bag.

"Get the Haldol!" Dawson screamed at Shay. Shay fumbled for it in the bag and quickly filled a syringe. Dawson snatched it from her hands as soon as she was finished, jamming the needle into Severide's neck and pressing the plunger down.

Kelly didn't even register the needle, but thirty seconds later his grip on Casey relaxed and he dropped like a sack of potatoes into Capp and Mills' arms.

Casey had blacked out just seconds before Severide dropped, and Otis and Herrmann caught him before he hit the floor. Dawson immediately went to Casey to check for a pulse, while Shay checked Severide's vitals.

"Got a pulse, he's breathing," Dawson said with relief.

"Same here," Shay replied.

The EMTs and firefighters all exchanged glances before Herrmann finally shouted:

"What in the HELL just happened?"

"Kelly?"

He could hear a muffled voice calling his name but he couldn't pull himself out of the darkness.

"Kelly can you hear me?"

The voice was familiar, and he struggled to wade through the haziness.

"Come on Kelly, wake up, please."

He finally recognized the voice, and it seemed to snap him into waking. He blinked a few times.

"Shay?" he looked at the blonde EMT and then around the room. She answered the question he was thinking.

"You're in the hospital," she said, scooting to the edge of the chair she'd set up next to his bed. He gave her a confused look. The last thing he remembered was talking to Casey as they walked back to their trucks from the house fire.

"When that guy tackled you at the house fire, and your mask cracked, you were exposed to PCP," she explained calmly, grabbing his hand. He blinked at her.

"What?"

"PCP," she repeated, "angel dust, whatever you want to call it, that's what that tweaker and his buddies were making in the house. You inhaled some, and it caused an," she paused, looking away, "adverse reaction."

"Shay," his voice cracked, his throat was dry. Shay handed him a cup of water and he drained it before he continued. "What happened?"

Shay looked at the floor and didn't say anything.

"Shay," Severide repeated, more forcefully this time. "What. Happened?"

Shay looked at him so seriously it scared Severide.

"You almost killed Casey," she said finally. He stared at her for a long time, heart pounding, his chest felt like it was going to explode.

"Where is he?" he finally said, making to get out of bed and go find his friend.

"Kelly, relax," Shay said, standing and trying to keep the man from getting up.

"No, Shay! I'm not going to relax! You just told me I almost killed one of my best friends! Now where is he?!"

Dawson, Herrmann, and Cruz had set up camp in Casey's room. Dawson sat with her head in her hands, eyes closed, in a chair on his right side. Herrmann had taken up a chair on the other side, and Cruz leaned against the wall near the window opposite the door. All three looked up as Shay wheeled Severide into the room in a wheelchair.

"Jesus," Severide breathed as he took in Casey's appearance. An angry, deep purple bruise covered his left eye, a gash along his left cheek was covered with butterfly bandages, and a small patch of gauze covered a gash above his right eye.

But the worst part was his throat. On either side of his neck, Kelly could clearly make out deep bruises in the shape of fingers.

His fingers.

Kelly felt like he was going to be sick.

"Yeah, you did a number on him Severide," Cruz said softly from across the room. Shay glared at him.

"Can we get the room for a minute guys?" she said with barely veiled annoyance. Herrmann gave Cruz an irritated glance before he rose and exited the room, Cruz in tow. Dawson stayed in her chair, looking over at Severide as Shay wheeled him up next to her.

"How are you feeling Severide?" she asked softly. She sounded genuinely concerned, not a trace of blame in her voice. Severide didn't take his eyes off of Casey.

"I almost strangled my friend," he replied. "How do you think I feel?" Dawson and Shay exchanged an unreadable look, but before either one could say anything, Casey groaned and shifted slightly.

"Casey? Casey man, can you hear me?" Severide leaned closer to his friend, putting a hand on his ankle.

Casey slowly came into consciousness, taking in the room around him and the people staring down at him.

"What's going on?" he asked, as though they were all standing in his bedroom rather than his hospital room.

"You're in the hospital," was all Dawson could think to reply. Casey blinked a few times and looked from Dawson to Shay to Severide, his brow furrowed as he noticed Severide's wheelchair.

"How did-" he started to ask, but as he stared at Severide it was like the memory came rushing back. Severide slowly retracted his hand from Casey's ankle.

"Kelly came into contact with PCP at the scene after the tweaker took him down," Shay said by way of explanation. "We think you just happened to be the first person that talked to him after the effects kicked in." None of them said what they were all thinking: that PCP only caused a violent reaction if the person had a reputation for aggression.

Casey locked eyes with his friend, Severide looking like he'd break under the weight of his guilt.

"I'm so sorry Matt," he said cautiously.

"Can I talk to Severide for a minute guys?" he said in response, looking up at Dawson and Shay. They both nodded, Dawson squeezing Casey's hand before heading for the door. Casey watched the door close behind them before he looked at Severide again.

"I'm so sorry man," Severide repeated, the words spilling out. "I don't know what happened, I just- it was like I couldn't control my body, and when I saw you, I just- I don't know," he trailed off, looking down at the floor.

Casey was quiet for a moment. Severide was envisioning having to transfer shifts or houses, if Matt couldn't forgive him he couldn't forgive himself and there was no way he could continue to work side by side with someone who didn't trust him.

"When you saw me, you thought about Andy," Casey said finally. Severide looked up sharply and started to protest, but Casey held up a hand to stop him. "I get it. Because that's what I think about every time I see you. The fact that it's just you and me now. There's a little part of me that can't let go of the guilt and the blame and," he paused, finding Severide's eyes, "the anger.

"So I think I know what happened. A little bit of PCP, combined with your naturally aggressive personality, add in some residual anger and here we are," he finished, gesturing at the hospital bed.

Severide just sat silently and considered the man before him. It was true, that despite the time that had passed, there was a small part of him that was still angry with Casey. It was unfounded, sure, and he knew that. But his best friend was still dead, and part of him still wanted to blame Casey because that was the less destructive option than blaming himself.

"It's okay Kelly," Casey said, giving Kelly a serious look that conveyed his forgiveness. "Next time though, let's just duke it out in the ring, alright? With gloves," he groaned and leaned his head back on the pillows.

"You got it buddy," Severide chuckled.