Stella's ex appears and may cause trouble in the upcoming premiere episode, titled "The Hose or the Animal," of the fifth season of the American action drama "Chicago Fire."

Severide (Taylor Kinney) and Stella (Miranda Rae Mayo) are extra cautious and on the lookout for her unstable former boyfriend, Grant (Guy Burnet), who also departed Chicago Med without prior notice. Meanwhile, Dawson (Monica Raymund) realizes that she is now responsible for Louie (Aiden and Austin Cohen). Because of her parental responsibilities, she questions herself whether to continue her dangerous career path as a firefighter.

Casey (Jesse Spencer), on the other hand, is back to working as Alderman. However, things between him and his political consultant, Susan (guest star Lauren Stamile), seem to not be doing well. Meanwhile, Borelli (Steven R. McQueen) continues to deal with his problems, as well as blame Chief Boden (Eamonn Walker) for his brother's demise. With all the problems piling up, he may reach his breaking point. Plus, Mouch (Christian Stolte) and Brett (Kara Killmer) decide to create a new venture together.

The promo trailer for "The Hose or the Animal" shows the firefighters on duty while saving lives, as well as living their normal everyday lives.

In one of the sneak previews, the firefighters are seen responding to a fire from a garbage truck after it collided with a school bus. As they inspect the school bus, they discover two boys who are still stuck inside, and one of them is pinned by a metal bar.

Series executive producer Michael Brandt revealed on TV Guide that Mouch has a secret talent that viewers can see in the premiere episode. "He's secretly been writing firehouse-based romance novels," he said. "You can imagine when Platt does find out that he's been doing this and he's been doing it with the cute blonde in the firehouse that Platt might not be so happy about it."

"Chicago Fire" season 5 premieres on Oct. 11 at 10 p.m. on NBC.