After a slew of brutal slayings, District 21, led by Sergeant Hank Voight go after a Columbian drug cartel cleaning house in Chicago. They discover D’Anthony who proves to be an asset in the investigation. At District, complicated histories and unit rivalries surface which could end up costing them one of their own. Meanwhile, Rookie Kyle Ruzek is pulled from the police academy by Olinski to join the team.
Antonio’s son was kidnapped and he has a feeling the Columbian drug gang is to blame. Pulpo, the Columbian gang leader, is being held in jail and suggests his release may trigger the release of Diego. During the investigation, Halstead learns some new information about Lindsay. Voight offers Antonio a new approach to get information on Diego’s whereabouts.
Voight and team head to a house that’s been associated with a number of top gangs. Events at the search result in Ruzek, being encouraged to seek some counseling which may have lasting repercussions professionally and personally. Meanwhile Halstead’s temper rises when he comes in contact with some unwelcomed people from his past.
More is learned about Halstead’s dislike of the Rodiger family and it’s family relationships all around as Olinsky shows a paternal side with his daughter Lexi in an attempt to protect her and as Voight’s trying to help his son who has recently been released from jail. Meanwhile the Intelligence Unit investigates a counterfeiting operation after discovering some high end cloth-like paper. Sergeant Platt sends Atwater and Burgess to arrest a hoarder where they discover more than just clutter.
Atwater and Burgess are given a new patrol car, but are challenged with keeping it brand new. A run in with a psychotic woman leads the Intelligence Unit to discover a drug smuggling operation which has put several girl’s lives in peril. Voight’s overprotective act with Lindsay leads her right where he doesn’t want as she also helps to keep Justin out of trouble. Meanwhile on stakeout, things get tense between Olinsky and Ruzek as Olinski tries to teach him the finer points of surveillance.
The Fitori murder case is brought to the intelligence unit and Voight’s son, Justin, may be involved. Gradishar fills Antonio in on the arrangement between Internal Affairs and Voight which increases friction between Voight and Antonio. Back at the precinct Ruzek helps Burgess get back at desk sergeant Platt.
Voight is assigned a new Internal Affairs handler, Stillwell who proves to be suspicious of Voight’s actions. During an investigation involving a gambling ring Voight is forced to work with his former partner from the Gang Unit, Shi. At the same time Halsted remains fixated on Lonnie Rodiger and enlists Jin’s help to gather more information. Meanwhile, Ruzek’s inflated ego leads Olinsky to take him down a peg and offer a great opportunity to Atwater.
In responding to a call Atwater and Burgess discover a gunshot victim and the only witness is Lexi Olinsky. The shooting is tied to a Latin gang. To protect Olinsky’s daughter, Voight takes the case from the Gang Unit. Ruzek pulls up Burgess to help with an undercover mission that he hopes will help solve the case.
Voight pulls Halstead's badge when Lonnie Rodiger is found dead. After a car accident Severide and Clarke discover the torso of Dr. Elliot who has been instrumental in putting away high profile criminals. With Intelligence down one Sumner is given an opportunity to prove herself. Meanwhile during all the investigation Lindsay and Severide share a moment.
Voight and the team discover a massacre, eight million in cash stolen and two wounded men in a clearing house. During questioning, one guy, Perko, provides some intel that is key to the case and leads Antonio to realize that two gangs were involved. Burgess steps up to help the unit and prove herself to Voight. Meanwhile, a softer light is cast on Platt when she enlists the help of Ruzek.
Commander Perry notifies the Intelligence unit that Pulpo has been released to help track down a dangerous cartel leader. This doesn’t sit well with our team as he kidnapped one of their own and no love is lost between sides. Meanwhile, Ruzek gets some difficult news as a blast from Lindsay’s past comes back, giving us a glimpse at where she came from. Voight reminds her that she’s come too far to screw it up. At the same time we learn something about Jin that is bound to be a problem.
As Antonio’s life is now in question, Voight and Platt open up about their pasts. Jin is caught while tinkering with Voight’s computer and uses the only scapegoat possible to keep him in the clear. At the same time with Charlie back in town Lindsay realizes she’s going to have to come clean about a few things. Halstead finally gets answers he’s been wanting about Voight’s and Olinsky’s past.
As the Sheldon Jin murder investigation moves forward, Voight is under close watch by Internal Affairs but he’s still in complete command of the intelligence unit. A routine undercover job becomes anything but when Voight’s SUV is T-boned while trailing an armored car carrying Ruzek. Burgess meets her new partner, Sean Roman and tension is high from the start, and she soon realizes there’s more to his story. After a long day, Lindsay pays a visit to someone she hasn’t seen in a very long time.
Intelligence begins to look into a string of murders where the victims have a dollar bill pinned to their chests. Thanks to some digging by Ruzek, Voight learns his friend was involved in some shady business dealings. Antonio and Halstead follow-up on some leads that help focus in on the culprit and motives for the murders. Burgess and Roman investigate a series of house break-ins and get some help from Desk Sgt. Platt.
The bounty on Halstead’s head becomes a serious reality as an innocent bartender takes a bullet meant for him. Olinsky tries to reason with Bembenek to call off the hit. Voight and the team keep this investigation in-house to find the hired assassin. After a tense interaction at district, Platt and Nadia come to an understanding.
Two teenage girls have gone missing and the team know the clock is ticking to find them. Halstead, Antonio and Lindsay investigate a tenement which gives them a much needed lead. Voight brings the father of one of the girls to district in order to get some honest answers. Platt puts Roman and Burgess on gun buy-back duty where they ask questions when they aren’t supposed to.
Following the death of a 10-year old girl, the intelligence unit has one option to gain access to their suspect. Voight and Olinsky follow-up on a good lead to answer some questions about the shooting. Burgess and Roman show three boys around district thinking they are part of the Police Explorers program.
A friend of Nadia’s leads the intelligence unit to a huge heroin bust. Unfortunately this bust results in Olinsky arriving home to find the suspects are holding his wife. Voight and the team think they’ve found a common thread with the suspects but it’s not who they think. Meanwhile Burgess and Roman are given an assignment where they get paired with a K-9 officer, Jenn Cassidy who is Roman’s former partner and girlfriend.
With Burgess in the hospital after suffering gunshot wounds, the intelligence team is determined to find the people responsible. Lindsay delays her start on the federal task force so she can help with this case. Search of the house provides a lead and when a bomb is triggered a key suspect is found. Meanwhile the team takes turns watching over Burgess. Voight informs Burgess of a new opportunity that this affords her.
Bob Ruzek is the first to arrive on the scene of a double murder. Intelligence arrives to take over the investigation and tensions arise as Bob needs to hand over the case to his son and Voight. Lindsay's new gig has her planning a trip to Bolivia for an undercover investigation that could be for an extended amount of time. Burgess and Roman realize they need to put past events behind them so it doesn't jeopardize them going forward.
Commander Fischer updates Voight on a missing officer that Narcotics had deep undercover with a robbery crew. Antonio connected with one of the crew members years ago, so he's asked to reestablish contact to help them find the officer. Meanwhile, Roman and Burgess are dealing with a squatter situation and they enlist Chicago Fire's Mouch to help.
With a World Trade conference in Chicago, all members of intelligence are undercover in various protest groups to determine potential threats. Ruzek, infiltrates the Black Grid group and befriends Sierra. When she ends up dead intelligence is suspicious of an Argentine Secretary, Fabian Sosa. Voight and Olinsky question Sosa about the death and the team enlists Mouse to help with their tech needs in tracking Sosa. Meanwhile Halstead’s brother, Dr. Will Halstead shows up in town for an undetermined amount of time and is already stirring up trouble.
Intelligence responds to a drug robbery gone wrong and in their investigation it's revealed that the first person Voight ever gave his card to is linked to a double murder. Voight will fight to keep her family safe. At the same time, we learn the real reason why Halstead's brother Will came to Chicago. Meanwhile Desk Sgt. Platt takes care of a young girl at district.
After arriving in Chicago to assist Voight and the team with a rape/murder case that has distinct similarities to a decade-old case from New York, Sgt. Benson asks Fin and Amaro to help; the prime suspect asks for a meeting with Lindsay. (We Called Her Jellybean (1) Chicago Fire S03E21) (Daydream Believer (3) Law & Order: SVU S16E20)
When multiple people are shot inside an athletic club intelligence work to find and take down the shooters before there's any more victims. When they discover that all the targets were from the same law firm it's apparent that it is a case of corporate revenge. Now they need to find out what the motive for these killings. Atwater is dealing with his new assignment, while doing so he plays a key role in locating the shooters. Meanwhile Platt and Halstead are trying to approach Lindsay to see how she's coping with a recent death.
Retired Commander Perry enlists Voight and the team to help extract his cop nephew from a unit of corrupt officers who are robbing drug dealers. When things go bad Voight must take down a younger, more violent version of himself. Meanwhile, Lindsay struggles to stay clean. At the same time a woman from Olinsky's past reaches out to him.
While working at a sobriety checkpoint, Burgess finds a duffel bag full of heroin in the truck of a respected college professor who claims to know nothing about how the drugs ended up there. At District, Roman expresses his desires to become a Field Training Office to Platt, and Mouse sets Halstead up with an off-duty security job working for the attractive owner of a medical marijuana clinic.
While responding to a call of shots fired, Voight, Antonio, Halstead and the team come across a secret battered woman's shelter and discover the owner has been wounded and a resident of the shelter has been kidnapped. Burgess and Roman go undercover to track down a man robbing people by catfishing them on a dating app. Lindsay opens up to Halstead about her past.
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.
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.
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.
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.
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.
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.
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.
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.
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. (Deathtrap (1) Chicago Fire S05E15) (Fake (3) Chicago Justice S01E01)
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.
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.
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.
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.
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.
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.
The district is in a state of change - Lindsay has moved to New York- and the CPD is under scrutiny about the corrupt nature of its institution. Under the watchful eye of the city, the team attempts to bust a gun deal that quickly turns dicey when innocent civilians and children get involved. Tension erupts when Chief Lugo brings in Denny Woods to review the shootout, and Halstead becomes a key player in the outcome of the case.
While investigating a drug-related homicide, Intelligence is stonewalled by the 'no-snitch' culture of the neighborhood. And Atwater discovers a personal connection to the case. Meanwhile, the police's own code of silence is put to the test when Upton is asked about Ruzek's rough altercation with a suspect.
When Intelligence busts a meth lab run by gang leader Marshall Carter, they uncover a re-homing scam in which children adopted from foreign countries are abandoned, then sold online. Meanwhile, Atwater struggles with the difficult decision about whether to move his siblings Jordan and Vinessa to a safer environment outside of Chicago.
In the wake of several gang-related child abductions, Intelligence must race against time to find a kidnapped boy. Owing to their swiftness and military precision, the team scours the VA records and tracks the suspects to a former Army Ranger. With his previous experience as a Ranger, Halstead convinces Voight to send him undercover to try and get information from inside.
One of Voight's friends, Congressman Scott Graynor, is found passed out in his hotel room with a dead Ukranian girl. When Intelligence discovers the murder is connected to a sting and Burgess' boyfriend is working with the Feds, Burgess must choose between compromising her case or her boyfriend's case.
When Atwater disappears at the house of a convicted felon, the evidence doesn't look promising - with his belongings and his blood left behind. Intelligence rallies to rescue him before it's too late. And Atwater struggles for survival faced with not only his captor but also a difficult connection to his past.
When a gang from El Salvador infiltrates Chicago, Intelligence works with a visiting detective to put an end to the crew's brutal tactics. Antonio finds himself getting close to the Salvadoran Detective, Marcella Gomez, only to learn she has a hidden motive for being in Chicago. Meanwhile, Voight learns that the body of his son's killer has been found.
After Voight witnesses the kidnapping of a young woman with a mysterious connection to his past, Intelligence works to find a connection between her kidnapping and several bank robberies. Ruzek gets a tip that a grand jury has been summoned, putting Olinsky one step closer to standing trial for Bingham’s murder.
After zeroing in on a suspect responsible for bioterrorism, the P.D. prepares to undertake its biggest manhunt yet; Upton is torn between helping track down the perp and providing emotional support to a scared young girl who needs her. (Infection (1) Chicago Fire S08E04) (Infection (2) Chicago Med S05E04)
The team responds to the shooting of a 5-year-old girl and must work the case while facing new obstacles that come from the heightened attention on police reform. Atwater is targeted by a group of officers who want to hurt him for standing against the blue wall. Voight questions whether he's cut out for a new form of policing as he manages oversight from the CPD's deputy superintendent.
Voight and the team help Assistant State’s Attorney Nina Chapman pursue a drug runner who dodged prison years ago after Chapman’s informant mysteriously disappeared. The investigation takes a turn when Voight uncovers a damaging secret from Chapman’s past, threatening the investigation and Chapman’s career.
A month after Voight's close brush with death, Intelligence is overwhelmed with cases as they catch a high-stakes drug bust.