Casey is placed in a dangerous situation while working undercover to bring down a trafficking ring being run out of Nesbitt's club. The squad's high turnover rate results in an unwelcome surprise for Severide. Dawson recognizes that her life is about to change. A new candidate makes an unusual first impression. Residents band together to protest a drug den in their neighborhood.

Boden's job is on the line pending an internal investigation. Severide adjusts to Patterson, his new commanding officer. Dawson shakes things up at the work. Casey searches for important evidence in his investigation of Nesbitt. Herrmann tries to keep the peace with Molly's new neighbors.

Evidence that seems to exonerate Boden may not be enough. Brett and Chili find themselves in a precarious situation. The team responds to a stuck elevator in a hotel. Jimmy Borrelli's older brother wants him transferred to a different house.

The squad members come together to support one of their own. Herrmann tries to figure out how to reopen Molly's after it gets shut down. Severide digs deep into the arson investigation.

Boden offers to host a wedding at the firehouse after a fire destroys the original location, but it doesn't sit well with Chief Riddle, who also butts heads with Dawson over her ability to perform. Severide fights for his old position. Capt. Patterson finds himself torn between leadership and his colleagues.

Boden's new neighbor asks him for a favor that could have serious repercussions. Severide is upset when he's treated like a candidate by Patterson. Cruz is visited by a gangbanger who knows his brother. The team responds to a call that involves an 18-wheeler; and is thanked with tickets to see Rush.

Boden suspects his neighbor is setting him up; Severide, who's still on probation, receives a surprise visit from his father and also learns something about Patterson that could be a game changer. Romance blossoms at a fire department gala.

Boden believes Maddox is behind Serena's accusations. Severide reaches out to Jamie, who's Maddox's lawyer, in an attempt to help. Patterson questions whether Boden can remain chief. Brett and Chili suspect that a man passed out in a garden is connected to a previous call. Otis has problems with his social calendar.

Patterson fills in for Boden, who's trying to clear his name. Severide learns where Serena may be hiding. Herrmann and Otis give Freddie a job that keeps him close by. Jimmy and Chili draw more attention then either bargained for.