Chicago Fire season 4
Chicago Fire season 4NBC

Numerous changes will be witnessed at Firehouse 51, which will only stir things up when Chicago Fire season 4 premieres on Tuesday, 13 October at 10pm EST on NBC Network. Episode 1 is titled, Let it Burn, where actor Steven McQueen would guest star as Jimmy Borrelli, a new candidate for the squad.

The official synopsis for episode 1 reads as follows:

Lt. Casey (Jesse Spencer), who is at the center of an undercover operation to bring down a trafficking ring run out of Nesbitt's (guest star Eric Mabius) strip club, finds himself in very dangerous territory. Meanwhile, as a result of the high turnover rate on squad, Severide (Taylor Kinney) gets a rude awakening when Capt. Dallas Patterson (guest star Brian White) is brought in, much to Boden's (Eamonn Walker) dismay. Dawson (Monica Raymund) confirms her suspicions that her life is about to change forever and Jimmy Borrelli (guest star Steven R. McQueen), the new candidate, makes an unusual first impression. Elsewhere, citizens of Chicago band together to take charge of their neighborhood in protest of a drug den in their area, resulting in ramifications that severely hinder members of Firehouse 51, who are called to the scene to battle a blazing fire.

Click here to watch the episode via live stream. You can also watch it online here.

The third season ended with Gabriela Dawson finding out that she was pregnant with Matthew Casey's baby. The latter, who was working as an undercover agent -- to bring down a trafficking ring -- is missing, and Katia (a strip club employee) was found dead in his apartment.

Chicago Fire season 4
Casey and Dawson are expecting a baby in Chicago Fire season 4NBC

Showrunner, Matt Olmstead, has teased how Casey and Dawson were surprised with the pregnancy news, and how things will unfold for them in an interview with The Hollywood Reporter.

He said: "There's a lot of complications and drama to play in terms of, they weren't even a couple, really, and this news hits them. Then it's well, are you coming back with both feet because of the news or because you feel a certain way? What he went through makes him realize how special she is to him and how important she is to him.

"It affects her job because you can't be an active duty firefighter if you're pregnant so she has to move over to arson investigation. It's given us story engine really for the first six, seven episodes," Olmstead stressed.

To know what happens next, watch epsidoe 1 of Chicago Fire season 4 on Tuesday, 13 October at 10pm EST on NBC Network.