'Chicago Fire' season 4 spoilers: Big changes coming to Firehouse 51 in season premiere

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Things will begin to sizzle right away for the firefighters and paramedics of Chicago Firehouse Department's Firehouse 51 in Tuesday's premiere episode of "Chicago Fire" season 4.

In the premiere episode, Lt. Matthew Casey (Jesse Spencer) will find himself in big trouble once again during his undercover operation regarding the trafficking ring that runs in the strip club owned by Jack Nesbitt (Eric Mabius.)

Based on one of the earliest trailers for the "Chicago Fire" season 4 premiere, Casey will not stop until he makes the trafficking syndicate pay for the death of Katya (Izabella Miko) and his abduction back in season 3. However, Casey's determination to take Nesbitt behind bars seemes to lack the support he badly needs since the feds are apparently involved in the case.

Meanwhile, Kelly Severide (Taylor Kinney) will find himself demoted at the start of the upcoming season. In an interview posted on Fansided, series executive producer Matt Olmstead revealed that throwing him off the lead is necessary to shake the story.

"We wanted to bring in conflict that was natural and organic, and you start to rotate through the people that have rotated through, and that's why he gets dinged. When he's demoted, it's humiliating," Olmstead claimed. "And his approach to it is that he can breeze on out of here, which he's good at, or am I going to fight for my life and is this worth is to fight for this house? Maybe I'm too aloof, and maybe I can get better at it. It really throws him in the deep end."

Severide will be replaced with Captain Dallas Patterson (Brian White) as the team's new supervisor this season.

The premiere episode of "Chicago Fire" season 4 titled "Let It Burn" will also introduce a new character named Jimmy Borrelli (Steven R. McQueen), who will report to work naked, thanks to the prank set by the team to welcome their new cadet. But Borrelli's entrance could possibly make a big mark on Paramedic Sylvie Brett (Kara Killmer) this season.

"Chicago Fire" season 4 premiere episode airs Tuesday, Oct. 13, on NBC.