Boden has a lapse in judgment in the aftermath of rescuing a young boy. Kidd struggles to win the approval of Severide's mom after a surprise visit and Otis takes on new responsibilities at the firehouse.

When the FBI takes over Firehouse 51 for an undercover mission, Casey and Severide volunteer to assist with the investigation. Kidd attempts to help Severide come to terms with recent developments he's been managing.

Severide faces some major adversity and Kidd is on a mission to help in any way she can. Following a car accident rescue involving a teenage girl and her young sister, a suspicious Brett has an unsettling feeling there is more to the story than what appears on the surface.

The big wedding day arrives and Firehouse 51 welcomes Casey back to celebrate the joyous occasion. Emma's plans to replace Violet come to a shocking end.