Tracy Spiridakos

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.

A rare but deadly bacteria takes its toll on numerous victims around the city, leaving Chicago's finest first responders to work together alongside the CDC to resolve the dangerous situation. Severide suspects something bigger is happening.

A spate of robberies comes to light after a firehouse lockbox key goes missing, and Sgt Hank Voight suspects a firefighter may be involved. With Boden's support, he recruits Cruz to go under cover to help sniff out any suspicious activity.

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.

Mouch builds a classic fire truck model for the Deputy District Chief, but quickly needs some assistance from Gallo and Ritter. Brett and Violet encounter multiple victims with a strange set of symptoms. The results of Cindy's chemotherapy loom over the Herrmann family.

An entire apartment complex is forced into quarantine when cases of the deadly virus turns into an epidemic.