The premiere episode of NBC's "Chicago Fire" season 4 titled "Let It Burn" will see Severide (Taylor Kinney) going through a problematic career, Casey (Jesse Spencer) being put in a threatening circumstance and Dawson (Monica Raymund) finding out that her life is about to go through some significant changes.

CLICK HERE to find out how the life of Casey, Dawson and Severide is about to change when they face an unexpected threat in the latest episode of season 4.

According to the synopsis of season 4 premiere episode, "Casey is placed in a dangerous situation while working undercover to bring down a trafficking ring being run outside of Nesbitt's club, and the squad's high turnover rate results in an unwelcome surprise for Severide.

"In other events, Dawson recognizes that her life is about to change; a new candidate makes an unusual first impression, and residents band together to protest a drug den in their neighbourhood."

In the last episode of season 3 titled "Spartacus," Casey was abducted and a girl was killed in front of him. In the new season, he will decide to go undercover as the girl was trying to reveal the whereabouts of the bad guys in season 3 finale.

In an interview with TVLine, executive producer of the show, Matt Olmstead, said that Casey was determined to go after the bad guys because the proceedings on the case were going slow as "the feds are involved and there are complications, which sends Casey through the roof."

He also said that even though Voight (Jason Beghe) will stop him from following his plan, Casey won't listen and will try his best to break into the gang so that he can avenge the girl's death.

It was also revealed in the previous episode that Dawson was pregnant with Casey's child. Due to her pregnancy, she may not get much action in the upcoming episodes. Casey doesn't know about it yet.

However, Olmstead further said that once Dawson lets him know about the baby, this will "pull him out of the quagmire that he has been in."