The men and women of the Chicago Police Department's District 21 put it all on the line to serve and protect their community. District 21 is made up of two distinctly different groups: the uniformed cops who patrol the beat and go head-to-head with the city's street crimes and the Intelligence Unit that combats the city's major offenses - organized crime, drug trafficking, high profile murders and beyond. The vast responsibilities that these jobs entail extend far beyond the walls of the precinct, often taking an emotional toll on personal lives of these men and women.
Intelligence investigates a gruesome case. Upon further examination, it appears the victim was wearing a CPD-issued wire at the time of his death. Meanwhile, Burgess meets her new partner, Julie Tay, who came from one of the worst assignments in the city. Together they respond to their first call, and Tay shares details of her past. Additionally, Commander Crowley confronts Lindsay about why she and Voight were at that location on the night that Intelligence pursued Justin's killer.
Made a Wrong Turn
When a call comes in reporting a car being stripped, Burgess and Tay respond and discover a badly beaten young man and his fiancé missing. Fearing a public relations nightmare Voight and the team are on their best behavior as they search for answers and the missing woman. At the same time, Lindsay surprises Halsted with a big question. Commander Fogel berates Platt for going over his head to have Tay assigned to District 21.
All Cylinders Firing
When Platt goes to her father Robert's house for dinner, she warns him to be careful with his new girlfriend Natalie. Following dinner, Platt is physically assaulted as she's getting into her car and is rushed to Chicago Med. Voight, Lindsay and Halstead arrive at the hospital to investigate, and a concerned Mouch finds himself being questioned. Meanwhile, Antonio leads the rest of Intelligence at the scene as they look into previous threats against Platt, but his attention shifts when he is called into Robert's townhouse and finds signs of an even more gruesome attack on Platt's father.
Big Friends, Big Enemies
When a car plows through a crowd of concert goers and gunfire erupts, Lindsay and Ruzek are on the scene. Unsure of the motive and concerned a terrorist group may be responsible, Voight orders in Homeland security, customs and the F.B.I. to assist. At the same time, Burgess spots Atwater's brother, Jordan, out where he shouldn't be. The team use their connections to throughout the city to bring some peace to the community before more blood is shed.
A War Zone
Intelligence is tasked with tracking down the dealers of fentanyl - a drug that has been linked to multiple overdoses around the city. As they investigate possible sources, the team uncovers a series of dealers in a college smuggling ring. Meanwhile, Tay and Burgess come across a bloodied child who exposes a dark and twisted secret about his home life with his parents. Additionally, Mouse causes tension as he looks to reenlist in the army, and Platt tells Tay that she has been reassigned to her original post.
After receiving a complaint from a frustrated neighbor, Burgess and Officer Sorensen arrive to the house of baseball player Jake McCoy, and find the dead body of a 16-year-old girl, Maya Collins. There is conflict within the case as Intelligence learns that Olinsky and McCoy are friends, and McCoy admits that he was helping Maya and other girls try to escape the sex trade. Meanwhile, Burgess and Sorensen track down a thief who turns out to be a cop with a rocky past, and Lindsay gets a mysterious flower delivery that may be tied to her past.
Voight calls the team to investigate a homicide involving the only witness in a rape and murder case against an extremely young man, Oliver Tuxhorn. Intelligence looks into Tuxhorn's family and their finances as they try to determine if someone was paid to take out the victim. Meanwhile, Stone offers Antonio a job as lead investigator for the state attorney's office, and Burgess and Sorensen's body cameras capture a bizarre exchange with a man that they pull over.
A Shot Heard Around the World
When a young officer is shot dead in the lobby of an apartment building, Intelligence looks to the latest known offenders who have threatened the police. But when a second officer is killed, the team finds that they are dealing with someone who is highly trained and knowledgeable. Voight works to keep the case contained as they deal with Chicago's ever-present war against the police. Meanwhile, Lindsay confronts Antonio about his new job with the State's Attorney.
Don't Bury This Case (2)
Severide is brought into the District for questioning after his car is found to have caused a deadly crash. As the investigation gets underway, the team works to uncover a group of car-jackers who may be the key to Severide's innocence. Meanwhile, Voight pairs Burgess with Olinsky, who has a hard time feigning his excitement about this new partnership, and Lindsay considers meeting her estranged father who is now out of prison.
Don't Read the News
After the body of young woman is found with multiple gunshot wounds, Intelligence uncovers details of her case that are similar to other deaths. They work to link all of these murders together to pin down the serial killer, and appease the families of the victims who have been looking for answers. Meanwhile, Lindsay decides to meet her biological father for the first time, and Voight welcomes Kenny Rixton to the team when Ruzek takes an undercover assignment.
When a mutilated sex offender is found dead, it is unclear if he was the victim of a hate crime, sexual assault or self-mutilation. As Intelligence questions those related to the case, they find themselves up against a private "special police" force who may be covering up illegal activities. Meanwhile, Halstead runs Jimmy's DNA to confirm that he is actually Lindsay's father.
After a female jogger is brutally murdered in the park, Rixton and Atwater arrive to see two suspects fleeing the scene. When the men make their way inside a church, the priest and parishioners gather outside to block law enforcement from entering. While investigating the case, Rixton gets caught in a lie with Voight.
I Remember Her Now
The body of a 15-year-old girl is found crushed in an abandoned building after she runs away from a treatment center for troubled girls. Voight sends Halstead undercover as a guard to work from the inside at the center, where he believes the girls are trading sexual favors for something in return. Meanwhile, Platt feels guilty because the victim was brought into the District last year, and Platt doesn't remember her.
When a charred body is found in a torched house, Intelligence must work to identify the victim, as well as a young boy who is found badly injured inside. As they look to determine the cause and who may have been involved, they are faced with a web of secrets and lies. Meanwhile, Lindsay and Halstead receive an odd warning about Rixton that leaves them suspicious.
Favor, Affection, Malice or Ill-Will
When Lindsay is tipped off about a grieving father looking to avenge his daughter's death, Olinsky goes undercover as a hitman-for-hire. With Gang Intelligence lacking enough evidence to arrest the original gang-banger in question, the team works to reinvestigate the case. Ruzek comes back after finishing his undercover assignment only to have Voight knock him down to patrol duty.
Emotional Proximity (2)
Olinsky's daughter remains in critical condition following a massive fire - leaving Intelligence on edge, but more determined than ever to track down the suspect. Voight opens up the case, knowing that he has Stone and his team's full support in the investigation, and all of Firehouse 51 behind him to examine potential origins of the fire. Intelligence works to connect the dots between the building owner, those who were inside, and a string of potential suspects.
Remember the Devil
After being tipped off about a woman running barefoot through the woods, Intelligence is led to a kidnapping victim locked up in a shipping container. The bizarre scenario leaves Voight questioning the legitimacy of the case, and sends the team on a twisted trail to get to the bottom of it. Meanwhile, a former relationship of Halstead's comes back into the picture, much to the surprise of Lindsay.
Little Bit of Light
When Chicago's "Night Crawler" Bobby Trent is murdered over a single piece of mysterious footage, Intelligence must investigate one of Chicago's wealthiest families -- uncovering a lineage of old money and secrets. Meanwhile, Burgess's sister Nicole arrives at the District for a visit, and presents an icy attitude towards Ruzek.
Last Minute Resistance
After encouraging her sister to spend a night out with friends, Burgess wakes to find that Nicole never made it home. As the guilt begins to eat at Burgess, the team in Intelligence bands together to make finding Nicole their main priority. The case kicks into high gear when she is found clinging to life in an El station.
Grasping for Salvation
While investigating the murder of a teenage boy, Voight finds a connection with the murder weapon - linking it to a case that he worked on 17 years ago. While the victim's father, a prominent defense attorney, tries to get the case taken over by Area Central Homicide, Voight digs back into the old case under the watchful eye of his former partner, Lieutenant Denny Woods.
When the team is called to an in-progress bank robbery, they come across Detective Hailey Upton trying to take over the crime scene with her Robbery-Homicide unit - butting heads with Voight in the process. As the robberies continue to be executed around the city, Lindsay is forced to make a decision in the heat of the moment, revealing a surprising suspect behind the mask. While working on the case at the district, Upton is shocked to come across Platt, who has a special connection to her past.
Army of One
A live video is streamed online showcasing a tortured man being beaten and burned alive. Upon further investigation, the victim's identity is traced back to that of a man who had been previously locked up for statutory rape. When another attack of a similar nature occurs, Intelligence finds a connection between the crimes, suspected pedophiles, and group named the Perv Hunters. Meanwhile, Lindsay runs into a few bumps in the road - both personally and professionally.
Fork in the Road
In the season finale, when Lindsay receives a panicked call from her mother Bunny whose boyfriend had just been shot, Lindsay must figure out the best way to approach the situation, as her mother is now a murder suspect. The case opens up when a group of high school students OD, and the drugs in question relate back to the situation with Bunny. In addition to her mother's issues, Lindsay finds herself up against the review board dealing with consequences of her actions.