Many actors in the franchise appeared outside of their main series guest starring in the other part of the crossover.

series regular Brian Geraghty who portrays Sean Roman and last appeared in the franchise in 2016.

Ambulance 61 is dispatched to a call, when they arrive they find multiple people down of suspected opioid overdoses.

The Intelligence Unit starts investigating where the drugs came from and it is found all the victims have suffered from counterfeit Oxy.

officer Sean Roman shows up at Firehouse 51 looking for his sister Sarah, who was friends with the original victims, and went missing a week prior.

Boden tells his wife Donna, who is a teacher at the victims school, about the deaths who takes it hard.

Casey and Severide go inside to search the house and find Butler suffering from a gunshot wound.

Neighbors identify Butler heading inside the house with a can of gasoline and is assumed to have started the fire.

Burgess and Roman interview Peters' ex-roommates who identifies Sarah and points them to a lake house.

A witness near the warehouse at the time of Peters murder identifies a black Range Rover driving away from the scene that points Intelligence towards a house where they find another suspect.

Burgess re-questions the witness who identified the Range Rover but he doesn't recall seeing a blue Nissan.

series regular Brian Geraghty would return to the franchise as a guest star for the event.

that airs in the second half of the television season; Chicago Fire showrunner Derek Haas stated "We do two crossovers a year, typically a gigantic one in the fall and then a Fire/P.D.

[7] Lerner later mentions that she enjoyed the unusual pairings between characters Kelly Severide and Sean Roman because of their similarities and said that overall this crossover event was disappointing compared to the previous one.