Chicago P.D. - Season 4

4x02 - Made a Wrong Turn

On the hottest day of the summer, the Intelligence unit investigates the case of a missing woman in a notorious African American neighbourhood. Meanwhile, Platt is threatened by Commander Fogel over her decision to have Tay reassigned to the 21st District, and Mouse announces his plans to reenlist in the Army Rangers.

4x03 - All Cylinders Firing

The Intelligence unit investigates after Platt is attacked while walking to her car. As the investigation develops, the unit finds Platt's father beaten to death and that his much younger girlfriend may have been involved. Meanwhile, after Burgess lets a key piece of case information slip, Platt escapes the hospital to find her own justice for her father.

4x04 - Big Friends, Big Enemies

The Intelligence unit investigates a drive-by shooting that killed a local rap star. Voight initially suspects a terrorist group may be involved, but after the second shooting in gang territory, the unit considers the possibility that both crimes are part of a gang war. Meanwhile, Burgess spots Atwater's younger brother while out visiting potential shooters and targets.

4x05 - A War Zone

The Intelligence Unit investigates after a body and a bag full of fentanyl, a drug that has been linked to a string of overdoses throughout Chicago, wash ashore. Meanwhile, Platt informs Tay that she has been reassigned to her original post, and Mouse causes tension within the unit as he continues to try and have a felony charge dropped so he can reenlist in the army.

4x06 - Some Friend

Burgess and new partner Officer Sorensen respond to a noise complaint from a house, only to find a dead teenage girl inside. The unit investigates the murder, which turns out to be the home of famous local baseball player Jake McCoy, who happens to be an old friend of Olinsky's. After Lindsay mysteriously receives an arrangement of daisies, Halstead tracks them to a florist near Leavenworth Penitentiary, a prison which Erin reveals her father has served time in.

4x07 - 300,000 Likes

The unit investigates the murder of a key witness in an ongoing high-profile rape trial. After pulling over an erratic driver, Burgess and Sorensen find the driver wearing a skirt, fishnet stockings and a chastity belt, recording it on their body cams. Sorensen later posts the video to his Facebook account. Meanwhile, Antonio is offered a lead investigator job at the attorney's office by Peter Stone.

4x08 - A Shot Heard Around the World

The Intelligence unit deals with a highly trained sniper who has targeted and killed two patrol officers. Meanwhile, having accepted Stone's job offer, Antonio deals with the aftermath of telling the team. Later at Antonio's farewell party, Voight offers Burgess a position in Intelligence. Also, Bunny drops a bombshell on Lindsay; her biological father is in town and wants to meet her.

4x09 - Don't Bury This Case

Severide is accused of a hit-and-run accident, which later turns into a vehicular homicide when one of the victims, a child, dies from her injuries. Lindsay and Voight suspect that Severide was set up while friendships and relationships are put to the test as the detectives and cops are forced to toe a very thin line with their friends at Firehouse 51 as the evidence against Severide mounts. Meanwhile, Burgess begins her first day in Intelligence and immediately clashes with Olinsky. Also, Lindsay contemplates meeting her father.

4x10 - Don't Read the News

The Intelligence unit investigates the murder of a young woman and later discovers that her murder may be connected to a potential serial killer who has murdered more than 10 women. Meanwhile, Voight introduces Kenny Rixton (guest star Nick Wechsler) to the unit as a temporary replacement for Ruzek while he is on an undercover assignment, and Lindsay finally meets her biological father.

4x11 - You Wish

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 that may be covering up illegal activities. Meanwhile, Halstead runs Jimmy's DNA to confirm that he is actually Lindsay's father.

4x12 - Sanctuary

The investigation of a jogger's murder in the park is blocked by a church offering sanctuary to the prime suspects. Rixton is caught in a lie with Voight.

4x13 - 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 centre for troubled girls. Voight sends Halstead undercover as a guard to work from the inside at the centre, where he believes the girls are trading sexual favours for something in return. Meanwhile, Platt feels guilty because the victim was brought into the District last year, and Platt doesn't remember her.

4x14 - Seven Indictments

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.

4x15 - Favor, Affection, Malice or III-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 gangbanger in question, the team works to reinvestigate the case. Meanwhile, Ruzek comes back after finishing his undercover assignment only to have Voight knock him down to patrol duty.

4x16 - Emotional Proximity

Olinsky's daughter is in critical condition following a massive warehouse fire. Voight investigates the fire's potential origins while Intelligence examines connections between the building owner, those who were inside and potential arson suspects.

4x17 - Remember the Devil

The Intelligence unit investigates a woman being held captive in a shipping container who refuses to help find the suspect involved. When a video goes viral, the team realizes that there is a second hostage, and they race against time to find her Meanwhile an ex-girlfriend of Halstead's turns up in Chicago and drops the bombshell that they are still married, and Olinsky returns to work following his daughter's death.

4x18 - Little Bit of Light

The squad deals with an upsetting case. Erin and Jay work through some difficulties in their relationship. Kim deals with personal issues when her sister, Nicole, arrives with some unexpected news.

4x19 - Last Minute Resistance

After a night out with friends, Burgess' sister Nicole is drugged and sexually assaulted. The Intelligence unit bands together to investigate the brutal attack, and soon find one of Nicole's friends is missing, only to later be found dead, having escaped the men who took both women. Lindsay and Burgess head undercover to draw out the suspects, and when one of the suspects tries to assault Burgess, the rest of the team moves in to make an arrest. Later, Burgess takes a temporary leave from Intelligence to care for her sister.

4x20 - Grasping for Salvation

When a teenage boy is shot dead, the Intelligence unit begins to investigate, soon discovering the gun recovered is the same gun used in a case Voight investigated 17 years earlier. As the victim's father, a prominent lawyer, tries to get the case taken from Intelligence, Voight digs into his past case, becoming suspicious of his old partner. As both Intelligence and Voight close in on the truth, Voight's ex-partner puts him up in front of the review board for disobeying direct orders.

4x21 - Fagin

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.

4x22 - 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 a group named the Perv Hunters. Meanwhile, Lindsay runs into a few bumps in the road - both personally and professionally.

4x23 - Fork in the Road

Lindsay's mother, Bunny, becomes a murder suspect when her boyfriend is shot; high school students overdose on drugs; Lindsay finds herself up against the review board.