In the premiere of this "Chicago Fire" spin-off following the men and women of the Chicago Police Department, the team discover an unexpected asset during their investigation into a drug-cartel cleaning house. Meanwhile, a rookie joins the team fresh from the police academy.
The unit mobilizes to find Antonio's son, who is believed to have been kidnapped by members of a Columbian drug gang whose leader is in prison. Meanwhile, Halstead gleans new information about Lindsay.
As the intelligence unit searches for the source of ammunition meant to kill police officers, Voight and his team investigate a house associated with major gangs. Meanwhile, Ruzek is encouraged to seek counseling; and Halstead has an unwelcome encounter with people from his past.
The intelligence unit goes after a counterfeiting operation. Meanwhile, Atwater and Burgess arrest a hoarder; Olinsky tries to protect his daughter; and Voight helps his son, who was recently released from prison.
The Intelligence Unit discovers a dangerous drug-smuggling operation. Meanwhile, Atwater and Burgess receive a new patrol car; Lindsay tries to keep Justin out of trouble; and Olinsky and Ruzek go on a stakeout together.
Two Special Victims Unit agents help Voight and Antonio investigate a series of rapes and murders. Meanwhile, Burgess tries to prove herself to Intelligence; and Lindsay gets back at a high-school rival with the assistance of Halstead.
The intelligence unit investigates the Fitori murder case, and it becomes apparent that Voight's son may have been involved. Meanwhile, Gradishar tells Antonio about an arrangement between Voight and Internal Affairs, which leads to additional tension; and Ruzek helps Burgess get revenge on Platt.
Voight works with a former partner during an investigation, and he's also assigned a new Internal Affairs handler who doesn't trust him. Meanwhile, Halsted seeks help gathering information about Lonnie Rodiger; and Olinsky attempts to deflate Ruzek's ego and offers a boost to Atwater.
Atwater and Burgess respond to a shooting involving a Latin gang, and they discover that the only witness is Olinsky's daughter. In order to protect her, Voight takes over the case, and Ruzek and Burgess go on an undercover mission that may lead to clues in the shooting.
Halstead is threatened with losing his job after Lonnie Rodiger is found dead. Meanwhile, Severide and Clarke discover the body of a doctor who helped put many criminals behind bars; Sumner gets a chance to prove her worth; and Lindsay gets a moment alone with Severide.
Voight and the team investigate a gang-related case involving several deaths and millions of dollars in stolen cash. Meanwhile, Burgess helps the unit in an effort to prove her worth; and Platt asks Ruzek for assistance.
The Intelligence Unit works furiously to find the people responsible for an explosion at Chicago Medical. Voight and his team use their own angles and connections; Lindsay and Antonio interrogate doctors who operated on an ambassador from Syria; and Olinsky finds a lead. Meanwhile, the team realizes that additional bombs may still be active; and Burgess waits to learn about her niece's fate.
The Intelligence Unit members are dismayed to learn that Pulpo has been released to help locate a deadly cartel leader. Elsewhere, Ruzek deals with difficult news; Lindsay has a brush with her past; and Jin faces a problem.
Voight and Platt share information about their pasts; Jin is caught poking around on Voight's computer and shifts blame to a convenient scapegoat; Lindsay realizes that she needs to be honest with Charlie; and Halstead gets the answers he's been seeking.
In the Season 1 finale, Atwater gets used to his new job while Antonio is stuck with desk duty during his recovery. Meanwhile, Lindsay asks Voight for help; and Jin is forced to come clean about his secret meetings with Stillwell.