Change is coming to Chicago Fire.

For a group that's seen their share of losses in colleagues and friends, it seems a new generation is getting ushered into Firehouse 51 with a baby on the way, a new chief and a new candidate. But before anyone can celebrate — or Gabby (Monica Raymund) will even share her news — the team will have to find Matt (Jesse Spencer), who has gone missing and has a dead body in his apartment. Severide (Taylor Kinney), meanwhile, will be resistant to new leadership, especially when his own authority is called into question. Will he retire his hose altogether? Executive producer Matt Olmstead teases what's ahead in Season 4.

Is Gabby's pregnancy a way to bring her and Casey together or drive them apart?
Matt Olmstead: Ultimately, it's a way to bring them together. Initially, there are a few hurdles to cross including the immediate concern that he's missing and there's a dead dancer in his apartment. Gabby realizes maybe this isn't the best time to let him know; so she has to hold onto this secret until he can get his feet on the ground, and when she tells him it's a big deal for them.

Why introduce a baby now?
Olmstead: We were at the fork in the road with [them] and we've gone through every permutation of what a couple can go through short of marriage and a pregnancy. We had to decide are we going to officially break them up and reset them both with other people? Or keep going forward with the bigger stakes of what a relationship could have. The testing really supported what we felt which was that they loved the characters individually and they loved them as a couple. We just couldn't picture them with other people. We tried, but they always had one eye looking at the other person, so we decided let's just go forward. But there's a lot of drama, conflict and joy to mine from her being pregnant.

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Severide had a rough season. Will he turn things around?
Olmstead: He's ready for some stability in his life, but unfortunately he does not receive stability in his life. In the very beginning of the season, he walks in and there is a new chief above Boden who is looking at all the people who have rotated through squad culminating in his friend Scott Rice who he vouched for and turned out to be a ducker. So they're not questioning him as a firefighter, they're questioning him as a manager. He's stripped of his lieutenantship and has to slide down a slot at squad table, and they bring in a character played by Brian White who's going to run squad. It's this ultimate indignity of, "I just got demoted, I'm no longer in charge of squad, I have to answer to somebody. Do I stick it out and suck it up and admit maybe there was some truth to what they're claiming and I'm a little aloof with my guys and work my way up? Or do I put a pin in this and work at another firehouse?" So that's his first thing and this major curveball which takes us through the first six or seven episodes. We pull the rug out from under him from the outset.

Will we see more of Brett (Kara Killmer) and Chicago P.D.'s Roman (Brian Geraghty)
Olmstead:
We have them crossing later. We have high hopes for [Brett] so we have a big story line early in the season. We're aware that Shay (Lauren German) and Dawson were a really great team and there was great chemistry there and we rotated a bit so we want to get some stability to [the paramedic] pairing. We also want to boost up Chili (Dora Madison) and Brett because they both replaced beloved characters and it was kind of a thankless deal. So we have a story line coming up with them individually and then as a pairing that will really show people what they're all about and get some investment into those characters.

On the Set: Go behind the scenes of Chicago Fire

And speaking of new characters, what can you say about The Vampire Diaries' Steven R. McQueen who is joining?
Olmstead: He comes in as a new candidate. We had Mills as a candidate and explored all the stuff a new candidate would go through and we had Dawson be a candidate, which was a bit different because it was through the eyes of someone we already knew. So we explored all the different versions [already], but it's a fact of life in a firehouse. So we wanted to bring a new character in with new complications, but we wanted someone who is really shot out of a canon and someone who... Casey looks at and says for the first time, maybe ever, "I've identified someone I want to train because this guy has a real chance to be a star in our department." So there are other things that are pulling back McQueen's character from accomplishing that, but in terms of Casey's investment in him, he wants to be this kid's mentor. So he's a really robust, natural firefighter who's free-wheeling. Having seen the first cut, [McQueen] is going to be a huge star.

Chicago Fire returns on Tuesday, Oct. 13 at 10/9c on NBC.