Severide considers an interesting proposition from a former firefighter turned medical student; Casey and Dawson face hurdles trying to permanently adopt Louie; Otis persuades Herrmann to throw a centennial celebration for the bar.
Patterson steps in as chief, and Dawson becomes a target of the conspiracy. Also, an act of violence changes Firehouse 51 forever.
Walker and the Rangers must protect a deaf girl from the mob when she accidentally witnesses the murder of an undercover police officer.
A gun battle erupts on the streets as Yokas and Bosco pursue a trio of thieves; Bobby implores his brother to turn himself in.