John Mossman

An investigation becomes personal for Voight when an acquaintance from his past is caught putting others lives in danger. A doctor with personal connections to Voight (Jason Beghe) is under investigation when four of his patients are committed to Chicago Med after an overdose of chemo. The doctor denies Lindsey (Sophia Bush) and Halstead (Jesse Lee Sofer) access to his files, but after obtaining a warrant the team is able to track down his patients and discover all of them have been poisoned with unnecessary chemo. Meanwhile, Burgess (Marina Squerciati) and Platt (Amy Morton) work together to clear Roman's (Brian Geraghty) name.

Stella Kidd returns to Firehouse 51. The team must work together to put out a potassium fire in a tunnel. After that incident, Ritter begins to worry about a young cop who witnessed the fiery death of a truck driver.