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.
Chili's erratic behavior puts a patient's life in danger; a tornado wreaks havoc on Chicago and Firehouse 51.