"Chicago Fire" finally released a trailer and a teaser, giving viewers their first look for the upcoming fourth season. The featured footage also gives viewers a taste of what's to come when season four premieres this October.

In last season's finale, Gabby Dawson (Monica Raymund) rushed to Matt Casey's apartment to tell him some good news. However, she discovers that the apartment has been ransacked, Casey is missing and there is a dead girl lying there.

Casey had gone missing after going undercover for Voight (of "Chicago P.D.") in order to bust a human trafficking ring.

"Chicago Fire" is set to return with an action-packed and emotional first episode, with Casey's fate finally revealed.

The first episode will go back in time to show what had happened to Casey and what events led to him being kidnapped. The "Chicago P.D." team will also feature heavily on the first episode as they try to save Casey.

After the tense and shocking events of the season premiere, the show will also have to tackle the implications that come with Gabby's pregnancy.

According to executive producer, Matt Olmstead, Gabby will have to make some adjustments at work. She will not be allowed to be a firefighter while pregnant. Instead, she can return to the ambulance or take on a desk job.

Gabby and Casey will also have to deal with the pregnancy together, even if they are no longer in a relationship with each other. Casey will initially be shocked with the news, but will try to deal with it later on.

Firehouse 51 also gets new additions this season who are bound to create some more drama and tension this season.

Fredric Lehne has been cast in a recurring role this season. Lehne will play Ray Riddle, the gruff and ambitious new Deputy District Chief. Lehne's character is willing to do anything in order to get the Fire Commissioner spot, even if it leads to the destruction of Firehouse 51.

Brian White will also be joining this season as Captain Dallas Patterson. He will take over as squad lieutenant after Severide (Taylor Kinney) was demoted last season.

Steven R. McQueen has also been cast as a candidate, Jim Borelli. The new firefighter is set to make quite an entrance on his first day. He will be late, duct-taped and toilet-paper wrapped as he is dropped off by his older firefighter brother. Captain Boden will not be pleased by this new addition to the house.

Rachel Nichols also joins the show as a potential love interest for Severide. After having been demoted, Severide is sent to a mandatory manager-training course and meets Nichol's character. "There's a little romance that happens there that turns into a complication down the road," Olmstead said.

"Chicago Fire" returns for its fourth season on Oct. 13, Tuesday, at 10 p.m. ET on NBC.