We were at a routine call, a fire in a trashcan that had got out of control and spread to the dumpster next to it. There were half a dozen homeless men, drunk and apologetic, edging as close as they could to the blaze for the warmth, even while the crew were trying to keep them out the way. Boden was on the verge of losing his rag with them and Casey, Herrmann and Otis were unsuccessfully trying to shepherd them away. I grabbed a bundle of blankets from the bus and went over to them.

'I got this,' I said to Casey, before turning to the men. 'Hi fellas, cold night eh?' I could feel Casey looking at me so I turned back to him. 'That ok Lieutenant? Do you need me somewhere else?' It was a bit of a dig, given that Mouch and Cruz were on the hose and there was nothing else to do.

'Good thinking, Dawson,' Casey said gruffly and left me to it. The men were standoff-ish at first, made a few gendered comments, but I'm so used to it that I waited until they were done, and carried on asking about their night, about whether they were staying here for the evening or whether they had somewhere to go. It didn't pay to jump straight in with the lecture, but there was a new shelter on the corner of West 33rd that I thought they might not know about.

The others were packing up the truck when I saw it: a flash of light in the opposite building. The building was an old block of offices, long derelict with shattered windows and graffitied walls. We were on the outskirts of Chicago, which wasn't really our domain but we'd been diverted to cover a busy night for another shift. Terry, one of the men, saw me looking. His wife had committed suicide after the death of his son, some twevle years ago.

'Don't mind that,' he said sternly, 'it's nothing. Nothing for the likes of you my dear. You done your job here, and we're sorry for any hassle we caused, but you leave em be. And you know what, you shouldn't come back here, not you my dear, it ain't safe for you inner city lot.' But then, unmistakably, I saw the warm flicker of a flame.

'Terry, what's going on up there?'

'Nothing, absolutely nothing.' The others were shuffling their feet, avoiding my eye.

'Terry, we have a job to do. I'm not about to charge up there alone, ok?'

'There's nothing going on, ok lady?'

'Well, I guess I'll have to go and check it out then.' I made to leave them.

'No! Wait…' So he told me about the comings and goings of the abandoned office, of the time they'd heard shooting in there, of the single men who came alone, let themselves in through the broken door and came out, days later. But the flicker of the flame was clear, and growing.

'Please don't go up there,' Terry said, grabbing my wrist.

'Terry, it's my job.' I shook him off, calling to Casey and Severide, who were closest, and to Boden, who was by his car. It'd been months since we'd broken up, but right here in the dead of night, in the middle of a Chicago winter and on some stupid trashcan call, I felt my heart skip as Casey looked at me.

'What's up?' He said evenly. It killed me, the cold professionalism that we both insisted on. I was as bad as him and I knew it – all yes, lieutenant, no lieutenant, three bags full lieutenant. What else was I meant to do? I pointed out the fire, told them about what Terry had said.

'If there's any chance it's occupied, we have to go in,' Casey said, always by the book. So along with Otis, Cruz and Herrmann, Severide, Casey and I made our way to the abandoned building. Terry and his friends followed us, trying their best to persuade us not to go in, but when we got to the door, they quietened and fell back. As a precaution, Boden had called it in to Chicago PD, making me wonder what sort of night Antonio was having.

Then we crowbarred open the door and went in.

I wish I'd listened to Terry.

Inside, there was a clear track through the dust, like the paths that deer carve in the undergrowth. Ahead, Casey and Severide put their heads together and then drew apart, nodding.

'Herrmann, Dawson, you're with me, we're going straight up to the fifth floor,' Casey said.

'Otis, Cruz, we're clearing the floors up to the fifth,' Severide said. We followed the path to the stairwell, leaving the others to recon the rest of the building. Casey called it in to Boden, talking in a hushed voice. Boden's voice came back, booming, making us all wince. There was something very unsettling about the building. I could feel the presence above us. I wished we'd waited until PD had arrived, at least.

'Casey,' Herrmann said, 'something ain't right. I got a bad feeling about this.' I was grateful, because he voiced exactly what I felt. It was taboo for us to mention instinct or gut feelings, we always had to be by the book, but it was stupid because we all felt it. A sixth sense, telling us not to answer a call.

'I know,' Casey murmured quietly, surprising me. 'But we've got to check it out.' At the fourth floor, I smelt smoke and my heart sank. At the fifth floor, we entered through double doors into what was once an open plan office, but was now just chaos, with light fittings dangling from the ceiling, toppled filing cabinets, desks piled high, computers with their screens kicked in. Paper scattered the floor, dirty with damp and footprints.

The fire itself was up ahead in the middle of the room. It wasn't big and had the weak red light of a fire that was in its initial stages. But all the paper worried me. We made our way towards it. I heard Casey clear his throat, then say:

'Firefighter, call out.' So much for going incognito. We circled around it, checking the exit behind us, shifting chairs as we went. 'Looks like it's just a cigarette fire,' Herrmann said to Casey. They were so intent on the fire that they weren't looking at what was beside the fire, on the desks that lined the window. Why would they? But having a brother in Chicago PD had familiarised me with things like this. I knew what the vials were, the instruments and the plastic containers, hell, the Bunsen burners.

'Casey! Stop! Look, they're cooking. This is a meth lab. We've got to go.' Casey looked at me, then at the desks, then back at me.

'Go, get out. Move,' he pushed Herrmann ahead of him, back over the chairs. I turned back to the double doors, just as they swung open again. Two men stood there. We all froze. The fire crackled weakly beside us. It was getting hotter with every minute, building moment.

'What the fuck?' One of them said, stunned. The men were clearly users as well as cookers. Their clothes were dirty, their eyes deep in their skulls. I was used to profiling people quickly from when I'd been with the ambo. I knew this wasn't going to end well. We were dealing with desperate men. I felt Casey pulling me back, getting himself between the men and me.

'We're with Chicago Fire Department, we need to get you out of here.' He said, putting up his hands. I felt a rush of love for him, for his stupid, pigheaded professionalism. The man put his hand to the waist of his jeans, where a gun was tucked.

'Casey,' I said, reaching out for him.

'We're just firefighters…' Casey said, taking a step back. Then the man drew his gun and shot him.

Hello! Hope you all enjoyed the first chapter… more to come. Just to clarify, Casey and Dawson aren't together in this but there will inevitably be some Dawsey at some point.

Also it's set completely apart from stuff currently going on in the series and my other story. I've just had it in my head for a while and I love diving straight in at the action. This is from Dawson's POV but I might switch it around at some point...

What d'yall think?

Peace x