Boden forces members of Firehouse 51 to pull themselves back together in the aftermath of a harrowing fire explosion. While Severide goes missing for one week too many, Casey works to track down his whereabouts. Meanwhile, Newhouse brings some unexpected news regarding one of Mills’ relatives while Herrmann and Otis make some new goals regarding Molly’s.
Lieutenant Severide returns to Firehouse 51, but he is clearly not his usual self and Dawson counts down the weeks until she gets started as a candidate at the Austin Firehouse. Meanwhile, Mills learns more about his father’s family and Herrmann asks the rest of the Molly investors to come up with some new ideas to turn the business around.
Fingers get pointed and tempers flare between members of Firehouse 51 and the Austin firehouse when fire trucks collide en route to a perilous call. Meanwhile, Boden has a plan to get Dawson her badge, but it comes at a cost. Elsewhere, Mills confronts his past and his future on the same day and the Molly's crew hits some hurdles starting up their new food truck.
Dawson starts her first day as a candidate and looks to find a balance with Lieutenant Casey inside the firehouse. Mills must come to terms with a future that doesn’t include the squad. Meanwhile, Severide confronts his demons in an unexpected way and the Molly’s crew has a date with the city inspector to make sure their food truck is up to code.
The three series will share a storyline about a child pornography ring that stretches from Chicago to New York and will arc over three episodes, beginning with "Chicago Fire" and continuing on "Law & Order: SVU" and "Chicago P.D."