Mouch and Ritter work together to solve a murder mystery. Severide and Cruz tackle a food truck fire. Gallo goes to see Hawkins about Violet.

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.

Kidd and Severide's honeymoon is interrupted by a dangerous person from their past. Kidd's former academy classmate joins Firehouse 51. Brett and Violet reflect on their relationships.

Kidd recruits Carver, Capp and Tony to help prepare her new lieutenant's quarters. Severide and Det. Pryma pair up to work a police investigation. Firehouse 51 fights a movie theater fire.

Det. Pryma asks for Severide's help on a case involving explosives. Gallo and Carver clash after Gallo improvises on a call. Violet encourages Brett to start dating again.

Severide struggles with the cost of helping Det. Pryma with the Martucci case. Gallo campaigns for Herrmann to represent 51 at the National Firefighter’s Association’s Winter Conference. A familiar face makes a shocking return.

Det. Pryma's case comes to an explosive end with Kidd and Carver's lives in danger. Brett installs an infant safe surrender box at 51. Violet is determined to take Emma down.