On October 7, 2019, NBC hosted a fun and interactive press day for the One Chicago franchise. The Wolf Entertainment franchise, started by television legend Dick Wolf, includes Emmy-award winning TV shows Chicago PD, Chicago Med, and Chicago Fire. With over 389 episodes aired as of October 2, 2019, the One Chicago franchise has clearly gained quite a loyal following.

Questions for the talent and producers present at the roundtable discussions revolved around a hot topic: the looming premiere of the 3-hour Chicago Crossover Event. We had the chance to sit down with Chicago Fire showrunner, Derek Haas, to get the inside scoop on the process and inspiration for the epic event.*

.Journalist: So let’s start by talking about the crossover.. I watched the trailer. It looks incredible. What’s the inspiration for it?

Derek: We’re always trying to do something different than we’ve done before. This year we thought “why don’t we get all three shows active in the first hour, so it’s really more like a decide-an-adventure, where it’s this story, this story, this story, and it’s all intersecting and weaving. It was Dick’s idea. He was like “let’s do some weaponized biological agent”. I was like “hm.. let’s run with that!”

So then Dick and I conceived the story over the 3 hours. I was going to write all three but then that became.. unfeasible. So I wrote the first one and then Med and PD took over after. We’re still shooting it, it’s not done yet! We keep realizing “oh, we gotta get more over here..” It airs in a week and a half so we’re cutting it a bit close to the edge.

Journalist: Is it because of what’s happening in the crossover that made scheduling it so hard?

Derek: So what happened is we scheduled it over 3 production weeks. Fire is on episode 5, Med is on episode 6, and PD is on episode 7. And that’s because we have the cast all having to go to the other shows. And then when you cut together action sequences, a lot of the time they’re shorter [in run time] versus page-wise. So if you wrote a 50 page script, typically speaking you would have 46 minutes in an episode and you cut it down to 41. Well, this one had so much action in it that you did a 50 page script and you only have 38 minutes and you’re like “oh man we’ve got to put 3 minutes in”. But what it allows you to do is you find holes in what you were missing. There’s times where we’ll be like “oh wouldn’t it be great if Casey looked over to the right for a second?”

Journalist: Biological terrorism is such an intense thing. Will it have any lingering effects into the rest of the shows individually?

Derek: I wanted to leave it open to Med and PD to do what they wanted to do. There’s a storyline going in the first hour that continues on into the series. We’re not going to make it apocalyptic event that carries over into the rest of the show.

Journalist: How has that process been collaborating with so many different people and different talents and different wants?

Derek: It’s always fun. I have a blast whenever we get the characters from the other shows on Chicago Fire. The very first thing that Dick asked when he was pitching this idea was “what if the first time we see evidence of this biological weapon is at a Chicago Bears game?” I said I went to a tailgate last year and it’s really one of the best tailgates in the country. What if characters from all three shows are tailgating together when this happens? And that was such a fun day to shoot. We were all at Soldier Field, there were 500 extras, with the cast from all three shows.. It was just so fun! They don’t usually get to work in that kind of situation together.

Journalist: Is there a character you’re especially excited to write for this season?

Derek: I really like writing all of them.. The Otis story still affects people. Even when you think oh, they’ve already moved on, you’re going to find that people catch a moment and it stays. That’s been fun to write. I like writing the funny stuff too. I told Dick at the beginning of the year, I was asked by a reporter over the summer, “what’s it like writing chicago fire after 8 seasons? Does it get formulaic?” And I said oh no no, it’s easy. You’ve just got to write action, suspense, romance, comedy, drama, thriller.. all in one hour and make people care! That’s the formula.

Watch the epic, three-hour Chicago crossover event, Wednesday, October 16, starting with Chicago Fire at 8/7c on NBC.

*The following is an edited transcript of the conversation.