Tracy Spiridakos

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.

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.

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 undercover to help sniff out any suspicious activity.

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.

Halstead and Marcel facilitate a trans-organ exchange; Asher and Cuevas help a sexual assault survivor; Choi and Archer treat a patient whose case could expose a fraudulent doctor; Grant and Maggie take a trip down memory lane.

An entire block of flats is forced into quarantine when cases of the deadly virus turn into an epidemic.