In part one of the crossover with Law & Order: During a house fire, Firehouse 51 rescues the owner from the cellar clutching a suspicious box, leading Lt. Severide to bring in Sergeant Voight and Detective Lindsey for further investigation. (Chicago Crossover (2) aired on Law & Order: Special Victims Unit, S16E07. They’ll Have to Go Through Me (3) aired on Chicago P.D., S2E07.)