When Kelton is found murdered, Voight's grudge against the mayor-elect puts him under suspicion. Upton and Halstead are eager to prove their sergeant's innocence, but the more evidence they gather, the closer they come to doing the opposite.

When Atwater goes undercover in a dangerous South Side drug syndicate, he learns there may be more to its kingpin than meets the eye. Halstead tries to join Atwater undercover, but finds himself at a disadvantage. Voight petitions the brass to show Ruzek leniency in his court case.

After a botched carjacking turns out to be something much bigger, Voight’s unit goes toe-to-toe with a smart drug kingpin who only works with women. New recruit Vanessa Rojas struggles with the transition from undercover to Intelligence.

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)

A murder in a Bulgarian neighborhood results in a challenging investigation when locals won't talk to police. Ruzek has a clash with a patrol officer.

The shocking murder of young boys affects Halstead. Crawford encourages Intelligence to use a new facial recognition software to help identify a suspect, but the plan backfires.

Voight pulls Darius in after Crawford asks Intelligence to investigate a dangerous drug, but there is little trust in the relationship. When their plan to nail a dealer goes awry and another CI is murdered, the team must make a tough decision about Darius.

After injuring herself while pursuing a suspect, Burgess receives a shocking diagnosis. A homicide case turns into a missing persons case, with a sinister twist. Voight has to decide between justice and the letter of the law.

Halstead's secret ongoing relationship with a woman connected to another case puts him in jeopardy.

As they await news of Halstead's fate, the team turns their attention to an illegal arms dealer. Atwater discovers his brother is in Chicago and could be tied to the case. Voight must deal with Halstead's shooter. Burgess makes her decision.

Ruzek and Burgess’s secret begins to have severe implications for their police work. A series of deadly acts of vandalism causes tensions to run high in the insular neighborhood of Canaryville. Atwater tries to reach out to his brother.

Voight makes a deal with Darius Walker to help bring down a rogue group of dirty cops dealing drugs that were supposed to be destroyed. Upton clashes with Voight and enacts her own form of justice.

After receiving a distressing 911 call, Burgess enlists the team’s help to track down a girl caught up in a sex-trafficking ring.

A homeless man’s murder leads Intelligence to a criminal who has evaded capture for years. Rojas has a troubling experience with a young mentally ill man.

Intelligence searches for the dealer who caused multiple overdoses and is connected to Roman's missing sister; the case becomes a homicide investigation when they find the dealer's dead body. (Off the Grid (1) Chicago Fire S08E15)

An armed robbery case quickly turns into a homicide investigation. When one suspect’s background suggests domestic violence, Upton is forced to reckon with her childhood. Voight and Halstead butt heads over Halstead’s righteous instinct.

Voight enlists the help of a reformed gang member to get a key witness' testimony in a murder case. More lives are put on the line as a gang war brews.

Intelligence does everything they can to build a case against the elusive leader of a drug ring, but things get complicated when Rojas realizes someone she cares about might be involved.

The clock is on when Ruzek witnesses a woman's kidnapping and the team races to put the pieces together. Burgess tries to connect with Ruzek outside of work, but he mysteriously distances himself from her.

Atwater goes under cover to take down a gun trafficking ring, but discovers an officer from his past is under cover in the same organization.