The victim of a murder-arson case is discovered to have been wearing a CPD issued wire at the time of his death; Burgess meets her new partner; Cmdr. Crowley questions Lindsay about the night intelligence pursued Justin's killer.
Voight and the team search for answers after discovering a man badly beaten and learning that his fiancee is missing; Lindsay asks Halsted a surprising question; Platt is berated by Fogel for going over his head.
After Platt is physically assaulted while getting into her car, she's rushed to Chicago Med, where Mouch finds himself being questioned; Antonio and the team look for previous threats against Platt.
Lindsay and Ruzek respond when a car crashes through a crowd of concert goers and a gunman opens fire; Burgess sees Atwater's brother somewhere he shouldn't be.
The body of a college student is found with a backpack full of a drug linked to deadly overdoses around the city; Tay finds a bloodied child with a dark story about his parents; Mouse looks to re-enlist in the army.
While responding to a complaint, Burgess and Sorensen find the body of a 16-year-old girl in a baseball player's (Billy Burke) house; Lindsay receives a mysterious delivery that might have ties to her past.
When the only witness to the rape and murder of a young man gets killed, the team suspects that someone was paid to take the victim out; Antonio receives a job offer from the state attorney's office.
A highly trained killer is believed to be targeting the police department; Lindsay speaks to Antonio about his job with the state's attorney.
Severide is brought in for questioning after it is discovered that his car has been involved in a deadly crash; Lindsay considers meeting her estranged father.
Evidence from the case of a young woman who was shot to death confirms the Chicago P.D. has a serial killer on its hands; Voight welcomes Kenny Rixton to the team when Ruzek takes another assignment.
The investigation into the murder of a sex offender leads to a private police force operating independently of the Chicago PD; Halstead checks Jimmy's DNA to find out if he really is Lindsay's father.
A priest and parishioners block law enforcement from entering a church where two murder suspects are suspected of hiding; Rixton is caught in a lie with Voight.
When the crushed body of a young teen who ran away from a treatment center for troubled girls is found in an abandoned building, Voight sends Halstead under cover as a guard to investigate the center from the inside.
The team investigates a home explosion that left a charred body, one injured survivor and no witnesses; Lindsay and Halstead receive a strange warning about Rixton.
Olinsky goes under cover as a hit man for hire after Lindsay is tipped off about a grieving father looking to avenge his daughter's death; when Ruzek returns from his undercover assignment, Voight puts him on patrol duty.
Olinsky's daughter is in critical condition following a massive warehouse fire; Voight investigates the fire's potential origins; intelligence examines connections between the building owner, those who were inside, and potential arson suspects.
A hiker leads intelligence to a young woman being held captive in the woods near Chicago; a former relationship of Halstead's comes back into the picture, much to the surprise of Lindsay.
The investigation leads Intelligence to one of Chicago's wealthiest families after a nighttime photographer is murdered over a piece of mysterious footage; Burgess' sister Nicole visits the district and presents an icy attitude toward Ruzek.
When Burgess realizes that her sister, Nicole, never made it home after a night out with friends, the members of the intelligence team make finding Nicole their top priority.
The murder weapon in the killing of a teenage boy is linked to a case Voight worked on 17 years ago; the victim's father wants Area Central Homicide to take the case.
Intelligence investigates armed bank robberies, which point to some surprising suspects; Lindsay is forced to make a decision in the heat of the moment.
A vigilante posts a video online of a man, previously locked up for statutory rape, being beaten and burned alive; Lindsay encounters some personal and professional problems.