'Chicago Fire' Boss Says 'Last 10 Minutes' of Season 9 'Will Drive Fans Crazy' (Exclusive)

Chicago Fire
Adrian S. Burrows Sr./NBC

Executive producer Derek Haas looks ahead to the 'big' season closer.

With only a handful of episodes left before the Chicago Fire season 9 finale, you can bet the drama is about to ramp up even more. Executive producer and showrunner Derek Haas revealed that they're "going big" for this year's season closer, which officially began filming in Chicago on Tuesday.

"We're going to have one of these gigantic last 10 minutes that drive our audience crazy," Haas tells ET. "I definitely enjoy building up to what feels like a giant ending to each season that makes audiences -- because you know they have nothing until October -- so you've got to have them thinking about it all summer long and yes, I do take pleasure in that."

As is customary on Fire, the final few episodes of the season promise to be jam-packed. But Haas dropped more hints on those last few minutes before Fire's summer hiatus begins.

"Really it's the last two episodes are the big [ones]. We kept our powder dry and are firing all the cannons at the end of the season. So these last two episodes are just going to be 'bang, bang, bang, bang.' And it's a finale where if you leave with 10 minutes left in the season, then maybe you can go on and say, 'That was a nice wrap-up. They did it. I can go home happy from the scum marks,'" he says. "But if you watch the last 10 minutes, you might be cursing my name all summer long."

"Some people should just be happy. Be happy that it was a good season and then what could possibly happen? And it's only 10 minutes," Haas quips, asking, "What could possibly happen?" The answer: a lot. Asked whether there will be life-or-death cliffhangers involved with potentially not everyone getting out of it the same, Haas played coy: "Maybe... There's going to be a lot going on."

On Wednesday's episode of Fire, Stella Kidd takes on her final shift before taking the lieutenant's exam, and it's a harrowing one, involving a teenage girl from Kidd's Girls on Fire program who's stuck in a dangerous, life-threatening situation. Putting Kidd through her paces via this last case before the test was the writers' way of showing the viewers that a promotion is well overdue. 

"All season long we've been building towards her taking the lieutenant's test and we thought months ago when we were breaking this down in the writers' room, 'Should we give her that last shift before she takes the exam to showcase her abilities as a leader so that it doesn't matter what happens in the classroom and in front of the panel that's going to decide her fate?' We want the audience to see why in a real-world setting she deserves this new rank and leadership role," Haas explains. "We wanted to throw the kitchen sink at her and have it be an emotional call -- and a literal call -- that she has to go on before that, and have one of these shifts that test every ounce of her abilities. And when you can have an actress like Miranda [Rae] Mayo, who you can [give] gut-wrenching emotion, as well as comedy, as well as physical presence and romance, she just nailed it."

Though Kidd may be emotionally and mentally ready to take on the responsibilities and pressures of becoming a lieutenant, Haas cautioned that even if she aces the test, her road to ascending to the new rank may not be smooth or easy. (Not that it has been.) 

"Whatever happens in the test, there's always politics involved with it. We saw when Boden was running for commissioner and when Herrmann wanted to try to be a lieutenant himself, we wanted to make the case to our audience that she's ready and let the chips fall where they may," he says. "In my mind, she should be the lieutenant. Whether or not that happens, that's still what's coming in the season."

Chicago Fire airs Wednesdays at 9 p.m. ET/PT on NBC. For more, watch below.

To stay up to date on breaking TV news, sign up for ET's daily newsletter.