While responding to a call of shots fired at a family residence, Lindsay (Sophia Bush) and Halstead (Jesse Lee Soffer) discover the only survivor is the youngest daughter who is traumatized. While Lindsay and Dr. Charles (guest star Oliver Platt) evaluate the girl and see if she can help identify the killer, Antonio (Jon Seda) and Olinsky (Elias Koteas) look into a pyramid scheme "self-help" group for potential suspects. Meanwhile, Platt (Amy Morton) tries to make the case to Commander Crowley (guest star Barbara Eve Harris) for Burgess (Marina Squerciati) and Roman (Brian Geraghty) to remain partners.
When the team finds the body of a widowed, single-mother in the trunk of her car, they are shocked to discover that the victim was in constant contact with Voight's (Jason Beghe) now-reformed son, Justin (guest star Josh Segarra). After Lindsay (Sophia Bush) and Voight find Justin has been attacked in the same manor and is critically injured, Antonio (Jon Seda) and the team know that Voight will be out for revenge. Meanwhile, Roman (Brian Geraghty) makes a difficult decision and Commander Crowley (guest star Barbara Eve Harris) has plans to make changes within the unit.
While responding to a call of shots fired, Voight (Jason Beghe), Antonio (Jon Seda), Halstead (Jesse Lee Soffer) 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. The team faces a challenge as the gunman is still at large and the identities of the women are kept confidential. Meanwhile, Burgess (Marina Squerciati) and Roman (Brian Geraghty) go undercover to track down a man robbing people by catfishing them on a dating app and Lindsay (Sophia Bush) opens up to Halstead about her past.
When a call comes in about a woman stabbing a man then fleeing the scene, Burgess (Marina Squerciati) and Lindsay (Sophia Bush) go investigate and find a young woman with the weapon in her hand. The suspect turns out to be a victim and she tells Olinsky (Elias Koteas) that she was held hostage for months and her kidnapper attempted to psychologically manipulate her into forgetting her identity while he physically abused her. The team sets out to find the woman's abductor before he can harm anyone else. Meanwhile, tensions are high at the station when Ruzek (Patrick John Flueger) accuses Roman (Brian Geraghty) of having feelings for Burgess.
While working at a sobriety checkpoint, Burgess (Marina Squerciati) 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. Voight (Jason Beghe) decides to hold off on charging the unlikely suspect and Olinksy (Elias Koteas) and Antonio (Jon Seda) follow up on a lead to see who is behind the drug smuggling. At District, Roman (Brian Geraghty) expresses his desires to become a Field Training Office to Platt (Amy Morton) and Mouse (guest star Samuel Hunt) sets Halstead (Jesse Lee Soffer) up with an off-duty security job working for the attractive owner of a medical marijuana clinic.
When a young boy is executed, Intelligence turn to the boy's parents for information and upon further investigation, discover the father has a criminal background and was a part of a local gang. After another shooting in gang territory, this time nonfatal, Lindsay (Sophia Bush) and Halstead (Jesse Lee Soffer) speak to the victim's mother to see if the two crimes are related and Mouse (guest star Samuel Hunt) works to find a connection. To honor the deceased young victim, Antonio (Jon Seda), Platt (Amy Morton), Roman (Brian Geraghty), Burguess (Marina Squerciati), Mouse and a number of other CPD officers and members of the community come together for a candlelight vigil.
Voight (Jason Beghe) convinces Deputy Crowley (guest star Barbara Eve Harris) to bring in his former cellmate, Eddie Little (guest star Clancy Brown), as a CI for the unit in order to help bring down a big-time cocaine supplier and his local dealers. Antonio (Jon Seda) is skeptical of this decision but Voight puts him at ease when he opens up about his time in prison with Little. Meanwhile, Burgess (Marina Squerciati) makes a difficult decision regarding her relationship with Ruzek (Patrick Flueger) and Roman (Brian Geraghty) devises a plan to help fund Platt (Amy Morton) and Mouch's (guest star Christian Stolte) wedding with the help of Firehouse 51
Lindsay (Sophia Bush) goes undercover in an effort to track down a rogue police officer targeting women leaving a local casino. When Detective Martin Watts (guest star Erik Jensen), who oversees all cases out of the casino, gets word of the investigation he becomes involved much to Voight's (Jason Beghe) dismay. After recent events, Burgess (Marina Squerciati) sets plans in motion to transfer Districts pending Platt's (Amy Morton) approval and Mouse (guest star Samuel Hunt) attempts to lift Ruzek's (Patrick Flueger) spirits by offering to set him up with a friend. Meanwhile, Antonio (Jon Seda) volunteers to take Roman's (Brian Geraghty) place in the upcoming boxing match against Jimmy (guest star Steven R. McQueen) from Firehouse 51.
When the decapitated body of a woman found in Lake Michigan is connected to Voight's (Jason Beghe) social circle, Lindsay (Sophia Bush) fears his relationship with the group may hinder his ability to approach the case objectively. Roman (Brian Geraghty) is having a hard time coping with recent events and an error in judgment causes him to make a grave mistake. Meanwhile, Olinsky (Elias Koteas) becomes upset when Antonio (Jon Seda) doesn't consultant him before making a decision that could affect Michelle's (guest star Madison McLaughlin) future.
A doctor with personal connections to Voight (Jason Beghe) is under investigation when four of his patients are committed to Chicago Med after an overdose of chemo. The doctor denies Lindsey (Sophia Bush) and Halstead (Jesse Lee Sofer) access to his files, but after obtaining a warrant the team is able to track down his patients and discover all of them have been poisoned with unnecessary chemo. Meanwhile, Burgess (Marina Squerciati) and Platt (Amy Morton) work together to clear Roman's (Brian Geraghty) name.
A suspicious person call turns into a murder investigation when Burgess (Marina Squerciati) and her temporary partner Price (guest star Travis A. Knight) discover the body of a dead man in an SUV. After Mouse (guest star Samuel Hunt) identifies the victim as the owner of a security company, the unit soon realizes there might be more to his story. Meanwhile, Roman (Brian Geraghty) takes Andrew (guest star Vincent Shuster) out for a memorable daytrip and Platt (Amy Morton) offers Ruzek (Patrick Flueger) some assistance. Halstead (Jesse Lee Soffer) and Lindsay (Sophia Bush) take a step forward in their relationship.
ntelligence sets out to find a missing teenaged boy who they believe poses a serious threat to the students at his wealthy school after finding disturbing drawings in his notebook. Meanwhile, Atwater (LaRoyce Hawkins) is eager to make a good impression on a prominent African American police Captain (guest star Eamonn Walker) and Olinsky (Elias Koteas) and Michelle (guest star Madison McLaughlin) find themselves in a difficult situation and turn to Ruzek (Patrick Flueger) and Burgess (Marina Squerciati) for help.
While Platt tries to manage a chaotic desk area, a man struggling to get her attention takes a drastic action and demands that the unit find his missing daughter. At the same time, Commander Fischer (guest star Kevin J. O'Connor) informs Voight that Bunny (guest star Markie Post) is bringing up new accusations on a case from his past. Lindsay urges her mother to fix the situation. Meanwhile, Antonio is shocked to learn a secret Olinksy has been keeping.
After surviving a hit against him, Voight is convinced the culprit is a criminal he and Olinksy once put away and is determined to catch him before he injures anyone else. At District, Atwater accidentally spills information about Ruzek's past which unsettles Burgess and Platt assigns Burgess and Roman a high society dog-napping case.