|Full Name||Katherine Brennan|
|Affiliation||Chicago Police Department (former)|
|Occupation||Police Officer (former)|
|Rank||Dep. Superintendent (former)|
|Seasons||6, 7 (11 episodes)|
|First Appearance||New Normal|
|Portrayed by||Anne Heche|
Brennan's first appearance shows her arriving to a crime scene, under the belief of Voight's lying about why he shot the man who ordered Alvin Olinsky’s death. She tells him it is being investigated as a homicide, leading for her to suspend Voight, who temporarily puts Antonio in charge of Intelligence.
Voight returns to the scene of the shooting, and realizes the presence of a surveillance camera that captured the incident. Unfortunately, Internal Affairs already got the footage an hour ago, with Brennan denying that they have it. Voight confronts Brennan, knowing she is using him for something. He still believes it’s so she can fire him, once again making reference to “white, middle-aged” cops; she once again denies this, and refuses to say anything about her motives.
Later, Antonio tells Brennan that it was Voight who made it possible to close the case. Brennan is thus motivated to apologize to Voight. She’s seen the film of the shooting now, conveniently, and is willing to persuade the powers that be that it was a good shoot, under the condition that Voight agrees to help her, help her boss get elected as Chicago Mayor. She wants him to close, or possibly not close, certain cases at her direction. Voight says his price for becoming her new “friend” is clearing Olinsky’s name so that Meredith can collect her husband’s pension.
Brennan has also made friends with Alderman Jason Collick and his wife, Allison; when the latter is murdered in True or False, she takes it personally, demanding Voight arrest someone by the end of the first day of the case. When Intelligence arrests an innocent man who kills himself in his detainment cell, Brennan becomes more afflicted, choosing to address the unit's officers were only following protocol, to which Voight agrees. During the time in which Intelligence finds out Collick is the man responsible for the murder, she is met with shock and anger; she sets up a meeting by the crime scene, and is immediate to tell her subordinates to "take him."
Her support for Brian Kelton as Mayor of Chicago comes to a head when she is threatened about previous allegations being released, and resigns from the Chicago Police Department in Confession. Since then, she acted as a confidential informant for Voight until Kelton ultimately won the election.
Brennan shows up to the scene where Kelton was murdered. Throughout the investigation, Intelligence learns that the cleared out an apartment of someone who was killed. It is also revealed that she took a gun and a car from the apartment.
Voight visits Brennan at her home and she tells him she "had to do it." Voight then leaves with the intent of giving her an hour to let her get her affairs in order. Detective Jay Halstead, suspicious that Voight left without arresting her, enters Brennan's house through the back door which was open. He finds her in full uniform loading a revolver. Brennan points it at Halstead, who draws his weapon at her, before turning it on herself, to Jay's protests; Detective Hailey Upton then enters and scares Brennan, who blindly fires the revolver into the ceiling before it is recovered by the two detectives.
Halstead and Upton then take Brennan into custody and place her under arrest for the murder of Kelton. Upon arrival in the motor-pool, Sergeant Platt starts to walk Brennan inside. Brennan stops and expresses her anger toward Voight because he told her he would give her an hour and lied to her. She is then taken to be processed, to Voight's barely controlled anger.
|Season 6 Appearances|
|"New Normal"||"Bad Boys"||"Endings"||"Ride Along"||"|
|Season 7 Appearances|
|Doubt||Assets||Familia||Infection, Part 3||Brother's Keeper|
|False Positive||Informant||No Regrets||Absolution||Mercy|
|43rd and Normal||The Devil You Know||I was Here||Center Mass||Burden of Truth|
|Intimate Violence||Before the Fall||Lines||Buried Secrets||Silence of the Night|