Season 4 Episode 11
"The Path of Destruction"
Chili's erratic behavior puts a patient's life in danger; a tornado wreaks havoc on Chicago and Firehouse 51.
Having survived the stabbing incident at Molly's, Herrmann (David Eigenberg) returns to work. No time for rest, though, as a tornado is barreling straight for Chicago. When the firefighters hit the streets, they encounter a massive amount of destruction and several victims in the tornado's wake. Things get particularly tense when the tornado touches down in Herrmann's neighborhood. Firehouse 51 takes a trip to Herrmann's house, and a relieved Herrmann finds that his family is okay.
Cruz (Joe Minoso) attempts to apologize to Herrmann for what happened with Freddie, but Herrmann insists he doesn't hold Cruz responsible - and that he'd like to put what happened with Freddie behind him.
Still broken-up with Borrelli (Steven R. McQueen), Chili's (Dora Madison) behavior grows more and more erratic. When Chili absentmindedly switches a vial of valium for a vial of morphine - and nearly kills a patient in the process - only Brett's (Kara Killmer) quick thinking saves the day. At Molly's, Dawson (Monica Raymund) learns from Antonio (Jon Seda from Chicago P.D.) the real reason behind Chili's unstable behavior: Chili's sister, Jelly Bean, was found dead in a drug den the previous week.
A Homeland Security agent enlists the help of Boden (Eamonn Walker) and Severide (Taylor Kinney) for a covert task. Using the tornado as a cover, Severide kicks down the door of an abandoned house and finds what appears to be a homemade bomb operation. Only one problem: the suspect is nowhere to be seen. Thanking Severide for his help, the agent tells him that her team will do everything in its power to find the bomb maker.