Season 4 episodes
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Fork in the Road
After Bunny shows ties to a deadly crime, Lindsay faces a professional and personal dilemma that could end her career in Intelligence.
Army of One
When an online vigilante group targets pedophiles, Intelligence must work to intercept a series of live-streamed killings.
A ring of alarmingly young bank robbers hits Chicago, raising concerns for the Intelligence Unit; who is the mastermind behind this group of delinquent teens?
Grasping for Salvation
Voight goes toe-to-toe with an old boss after learning that he may have caused an innocent man to serve a life sentence.
Last Minute Resistance
After Burgess' sister Nicole is brutally assaulted, the team lends their full focus to catching the rapist; Burgess takes an active role in the investigation despite Voight's concerns.
Little Bit of Light
A crime videographer is found dead, with his equipment and data destroyed - and the murder shows connections to a wealthy Chicago family with a long legacy; Burgess' sister Nicole visits while going through a tough time at home.
Remember the Devil
The team tries to catch a kidnapper whose victim isn't telling the full truth; Halstead hides a heartbreaking secret from Lindsay; Olinsky returns after suffering the loss of his daughter.
Voight and team conduct an investigation in search of an arsonist who killed dozens of partygoers in a factory fire; meanwhile, Olinsky copes with the possibility that his daughter will never wake up from her coma.
Favor, Affection, Malice or Ill-Will
On a tip from Lindsay's informant, Olinsky plays hit man to catch a man who wants to avenge his daughter's death; when it turns out his target is innocent, the team scrambles to find the real killer. Meanwhile, Ruzek's return shakes up the precinct.
A case of mistaken identity reveals a lifetime of deception; Platt faces a shocking health scare; rumors circle the team about one of their own, who may not be as trustworthy as he seems.
I Remember Her Now
After a resident of a young women's treatment center turns up dead, Halstead takes on an uncomfortable undercover assignment that puts his loyalties to the test.
Two young murder suspects achieve sanctuary in a church, leading to a standoff between Intelligence and parishioners and attracting heavy media attention; Voight will stop at nothing to ensure the victim's killer is brought to justice.
After a sex offender is found dead and mutilated, the Intelligence Unit realizes his injuries don't align with his cause of death, leading the team on an unexpected pursuit; Halstead forces Lindsay to confront the truth about her biological father.
Don't Read the News
A young woman's murder shows apparent links to a series of unsolved killings, but it may be more complicated than it appears; Lindsay agrees to meet her biological father, while Halstead insists on investigating his background.
Don't Bury this Case
After Severide is implicated in a hit-and-run and cannot recall the events of the night, Voight and the Intelligence Unit work around the clock to uncover the truth. Meanwhile, Lindsay considers the idea of meeting her father.
A Shot Heard Round the World
The police force is shaken after one of its own is targeted by a cop killer; Voight and team put everything on hold to identify the perpetrator from a long list of suspects and stop his violent rampage.
The State Attorney's office calls upon the Intelligence Unit after the only witness in a serial rape case is murdered; Peter Stone offers Antonio a surprising - and tempting - opportunity.
When a baseball player is the main suspect in a young girl's murder, Voight and team dig for the truth - and Olinsky, who has a history with the athlete, may be their secret weapon. Meanwhile, Lindsay receives flowers from an unknown party.
A War Zone
When an epidemic of heroin overdoses sweeps the city, Voight and team must trace the operation back to its leader; meanwhile, Mouse fights for the opportunity to rejoin the military, despite Halstead's attempts to convince him otherwise.
Big Friends Big Enemies
After a 16-year-old rapper is shot at his own concert, P.D. tracks social media in the hopes of preventing an all-out gang war; meanwhile, Atwater worries that his younger brother is at risk of being affected by gang violence.
All Cylinders Firing
After Platt is brutally attacked by a mysterious assailant, Voight and the rest of P.D. work around the clock to find the culprit and uncover the motive behind the vicious assault.
Made a Wrong Turn
Police-civilian tensions create obstacles for P.D. as Voight and the team search for a missing woman in a high-crime neighborhood; Halstead and Lindsay take a big step in their relationship.
After Voight is suspected in the murder of his son's killer, Lindsay becomes the target for intense questioning; Burgess gets a new partner with an intriguing history.