Starts in 2x07 "No Regrets".

I've wanted to write this as my first CF story, a S2 rewrite with my OC, because I love the show so much. (Not to mention Herrmann's comments about female firefighters ticked me off. But that's a couple of episodes away.) And I needed something to tie me over until 1/7/14…which can't come fast enough. #SaveCasey.

I'll be adding my own calls, drama and romance to this as well, but it will mostly be following the rest of season two. So I hope you like this.

Disclaimer: I don't own Chicago Fire.

Chapter 1 - No Regrets Part 1

The weather was cool against her skin as she shoved her hands deep into her coat pockets. The uncertainty of what lies ahead as she walked the length of the driveway into Firehouse 51 was long forgotten as she remembered that she was doing what she loved.

The outside of the station was quiet as she walked past the firetrucks and came up behind a man who was sweeping the entrance. He was wearing a "Candidate" jacket.

"Excuse me?" she cleared her throat. The man turned towards her and smiled. "May I help you?"

"I sure hope so. Can you tell me where I can find Chief Boden?"

"Yeah, I'll show you." he said.

She followed him closely as he led her into the firehouse and down a hall towards a back office. Once there she thanked him and lightly rapped on the cracked door. "Chief Boden?"

"Yes. Come on in." Boden stepped from behind his desk and held out his hand as he greeted the woman. A man in a grey tee stood up as well and Mackenzie smiled at the person whom she hadn't seen in some time. "It's a pleasure to meet you, Mackenzie."

"Likewise, sir." Mackenzie Collins says as she adjusted the duffel bag on her shoulder.

"Casey, this is-"

"Kensi?" Matthew Casey was surprised as he took in the sight of his childhood friend. He pulled her into a warm embrace. "It's good to see you,"

"You too, Matt."

"You two know each other?"

"Yeah, she's my sister."

Boden raised one eyebrow and Mackenzie spoke up. "We're not related by blood. But we grew up together and Matt is the closet thing I have to family."

"Well then," Boden said as he left his office to go gather the crew. "shift starts at the top of the hour. Casey, show her to her locker. When your finished come to the common room."

"You got it, Chief." Casey motioned for Kensi to follow him as he led her down a short hallway. "So how have you been?"

"Good, all things considered." she replied with a small sigh. The closure of the house she had been at since she became a firefighter was hard on her. And sadly there wasn't anything she could do to change that.

"Did the rest of your team get all set up?"

"For the most part. Two of them are still waiting for their reassignment."

"Well, I can't promise anything, but I think you'll get along with the guys on Truck."

Mackenzie scoffed. "They've managed to put up with you for how long? Shouldn't be too hard."

"Very funny." Casey said with a hint of humor. "Your gear is in the locker. I'll be in the common room."

"Thanks Casey."

Ten minutes later Mackenzie was ready with her auburn hair pulled back into a pony tail and her grey tee tuck nicely into her dark trousers. When Chief Boden began speaking to the rest of the group she waited in the hallway until she was called, praying silently that this wouldn't be like her first day on the job.

"Do to the closer of Firehouse 17, we are welcoming a new Lieutenant into this House. And," he added as the group clearly remembered the last time a new Lieutenant came into 51. "I trust you all will show respect." Boden paused and motioned Mackenzie to join him up front. She held her head high and scanned the room as the group took the sight of a new person in.

"This is Mackenzie Collins and she will be second in command on Truck. That is all."

Casey jumped to his feet and ushered Kensi over to meet the crew. "So with me on Truck we have Herrmann, Otis, Cruz, Mills and Mouch. Then on Squad we have Severide, Clarke, Capp and Vargas. And last but not least is our paramedics, Dawson and Shay.

"Guys, this is Kensi."

Kensi waved to the group, feeling slightly overwhelmed but very welcomed but the greetings she received. In the mist of it all the look of jealously on Dawson's face didn't go unnoticed, but she left it alone. "Hey."

"C'mon, I'll show you around."

A few minutes before roll call, Matt and Kensi were looking over the trucks. "Looks like the engine is loosing water."

"A couple seals are cracked." Cruz said. "Put in a request and the Wizard said it would be a couple of weeks."

Casey sighed. "Sure we've got that long?"

Mackenzie walked around the house with little to do. She helped out where she could but mostly observed. It wasn't her first day on the job, but being in a new house made it feel that way. At least for the first hour or so.

Glancing out to the front of the house, Kensi saw Clarke talking with a woman who identified herself as his wife. But the looks of the conversation, whatever she wanted to talk about wasn't sitting well with the fireman. Finally, Clarke left as roll call was approaching and she followed him to the break room.

"Hey." Chief Boden greeted them. "Our house has been under the microscope lately, and everyone in the room has handled it like the professionals I know you to be. And that is why 51 is still going strong." Everyone but Herrmann applauded, the sullen look clear on his face as he knew what the chief was going to say next.

"And that is why in good conscience I am to announce my retirement from the CFD."

The room grew quite. Heads hung.

"It's been an honor to serve with you."

The alarm sounded throughout the house. "Engine 51, truck 81, squad 3, ambulance 61, battalion 25. Railroad incident."

"Let's go to work."

The trucks roared down the road towards the destination, lights flashing and sirens sounding. Mackenzie sat in the back of 81 in-between Herrmann and Mills, picking out bits of the ongoing conversation between the members.

"Did you know?" Cruz asked Casey.

"McLeod's been pressuring him." Matt replied.

"We just gotta get this call over with and talk him out of it." Herrmann says.

Otis smiled. "This will be quick. Five bucks says it's another cell phone on the tracks."

Mackenzie shook her head as the truck pulled up closer to the wreckage, helmet in hand and ready to get to work. "Fifty says it's not."

"Chief, I'm seeing multiple commuter cars derailed, at least a hundred fleeing passengers and several fires including the cars and a building."

"Did the train go into the building?"

"We're gonna need more alarms, chief."

"We got the passenger car." Severide said as he gave his men his orders.

"Herrmann, recon the tanker and get a handle on the car fires. Collins, check over there."

"Check the cars for victims. We've got more in the warehouse."

"All companies be aware that the overturned tanker is filled with propane. Work quickly and let's get those people out of those train cars."

Mackenzie jogged over to the nearest car and began to help a few of the victims who had climbed out of the windows. "Easy, easy. I got you." she said as a woman was lowered by a man to the ground. "Can you walk?"

The woman managed a swift nod. "Okay, head over there and you'll be taken care of." She repeated these actions until she was sure the car was clear then went to the next car.

"I've got at least 30 people still trapped in here, the doors are jammed."

Kensi walked over to where Capp was trying to pry the doors open but to no avail. After Clarke had grabbed a power saw from the truck, he began to cut a path into the car. "Alright, alright that's good. Help me slide it open. One, two, three!"

As soon as the doors were open enough, people filed out as quickly as they were able. "Watch your step, sir. I got you."

"Just keep going. Don't stop, c'mon." They were moving quickly to get the people to safety, keeping in mind of the overturned tanker.

"Hey, hey come here." Collins said to a young man who had only a slight limp but otherwise appeared to be in good shape. "I could use your help. Here," she motioned for the man to put his hand firmly on a woman's arm. "I need you to keep pressure on this and keep her talking. Alright?"

"Yeah, yeah."

"Okay."

Suddenly part of the tanker exploded. "We need to get water on that tanker now!" Boden said through the walkies.

"Collins! You got this!" Casey yelled back.

"I've got it! Go!" Collins turned to the men as they ran the hoses over to the burning tanker. "Alright, we need to keep this tanker cool! Get water on those fires and shoot a line on top!"

Only seconds had passed before a whizzing sound reached Chief Boden's ears. He watched as a cap shot off and a stream of pressure was released near an unsuspecting Herrmann. Not thinking he lunged at the fire fighter and knocked him to the ground just as flames shot out.

"What was that?"

"The pressure release Valve's venting!" replied Herrmann. "Without it this thing is going to blow sky high!"

"We need to get these attack lines back. We're going defensive! Go back!"

I think I'm going to separate each episode into two parts and if you guys like this, updates will be on the weekends because I don't have work.

And here are Kensi's outfits. Remove () (http) :/ (www) . (polyvore) .com(/lt_mackenzie_collins) (/set?id=107595543) and (http) :/ (www) . (polyvore) .com(/lt_collins_never_alone_c1) (/set?id=107595965)

Thoughts? Your reviews are what writers (like me) live off of!