Tracy Spiridakos

Tensions run high between Casey and Herrmann when the firehouse responds to an apartment complex fire. After discovering something extremely suspicious during the call, Kidd and Severide do some investigating and get CPD on the case.

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.

Chief Boden unwillingly agrees to let Dawson and Brett go undercover; Kidd and Zach's relationship hits a bump; Cruz has a hard time expressing his true feelings for Brett.

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.

An airfield emergency triggers a deeper mystery involving a passenger plane, propelling the Intelligence Unit into a high‑stakes pursuit of the culprit, all under the sharp eye of the FBI.

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