Gillian shows Cal a videotape of D.C. police Detective Farr savagely beating a 9-6 gang member named Prince John, while Farr's partner, Detective Wallowsky, watches. Gillian got the tape from the Department of Internal Affairs, which is investigating Farr and Wallowsky - and knows about Cal's relationship with Wallowsky. Gillian is angry that Cal would jeopardize the firm's police contract to have a compromised cop in his pocket and warns him to stay out of this.
Cal immediately visits Farr at a police shooting range and asks about his relationship with Prince John. Farr walks away. Cal then accosts Wallowsky, says he's seen the video, and asks why IA is watching her - and what's she hiding? No answer. Cal says that if she knows what Prince John has on Farr, she's also a target.
Cal and Wallowsky find Prince John on his street corner, and she arrests him so that Cal can question him. Cal notices someone watches this from a window. After interrogating Prince John, Cal thinks Farr is on the take and that Prince John is in danger, but without any real charges to hold him, Wallowsky gives the gang member a ride home.
Ria is watching the videotape, noting that Wallowsky shows resignation and fear, when Cal interrupts. Gillian asks Cal if he believes that Wallowsky is clean. "Like you?," Cal sneers, referring to Gillian's having obtained the tape illegally. Then he takes a phone call: Prince John has been killed on the street.
Cal, Gillian, Farr, Wallowsky, and Jenkins from Internal Affairs are on the scene. Everyone questions everyone else, and Jenkins arrests Wallowsky because an eyewitness says that she was the shooter.
Cal visits Wallowsky in jail. She didn't do it, and she says that Farr is innocent, too. Then Farr visits Wallowsky.
Cal confronts Jenkins and after threatening to expose her dirty laundry, she agrees to let him question Farr.
Eli listens to the eyewitness' 911 call and tells Cal and Gillian that it's full of holes. Cal and Gillian visit the caller, Mrs. Phillips, and discover that her grandson and roommate, Luis, is a 9/6 member, who is suddenly called away. Cal and Gillian follow.
Another gang member named Stomper has been murdered, and Farr's already on the scene. Cal tells Luis that the same person killed both gangsters and - in return for a punch in the stomach to cover for his cooperation - gets Luis to admit Wallowsky is innocence. Cal tells Gillian that the killings stem from an internal gang conflict and that Farr has chosen sides. Cal wants I.A. to let him question the gangster on the scene who can't conceal his smile.
His name is Suarez. He gives Cal nothing and gets released. Cal asks for all the videotapes of Farr and Wallowsky's interrogations of 9/6 members. When Cal, Gillian, and Jenkins review the tapes, Jenkins says that if Farr is dirty, then so is Wallowsky. Cal tells Wallowsky that if she doesn't give up her partner, she'll be sent to county jail, where it'll be easy for gangsters to kill her.
Ria and Eli bring in Mrs. Phillips and have her watch an unrelated videotape. She tells Charles (who's switched places with Eli) exactly what's on the tape. Eli reenters the room, explains that this is "change blindness," and gets her to admit she saw Wallowsky before and after - but not during - the murder.
Cal gets Wallowsky released. She says that there are two kinds of dirty: Who you are and what happens to you. Meanwhile, Gillian, Ria, and Eli watch the interrogation tapes. It's obvious that Wallowsky knew Farr and Suarez had a deal, so how could Cal miss this? Eli says that Cal's sleeping with Wallowsky caused "change blindness."
Wallowsky's explanation is interrupted by the sounds of a car outside. Cal orders her to douse the lights in favor of candles, put on some mood music, and call the police. Wallowsky also grabs several guns from a hidden stash and hides in a closet. Suarez enters and fires a machine gun into a bed full of . . . pillows. Wallowsky drops him with one shot, and she and Cal leave.
Cal tells Wallowsky that I.A. leaned on Gillian to lean on him to give her up. And he was disloyal to his partner because she's loyal to a partner who's dirty. Wallowsky admits that Farr's been protecting Suarez because he's Farr's illegitimate son.
Cal confronts Farr, who's awaiting questioning by Jenkins, telling him that Suarez tried to kill Wallowsky, and now he's got to choose between protecting his partner or his son. After questioning Farr, Jenkins tells Gillian that Suarez killed Prince Paul and Stomper because he knew that they were blackmailing Farr, and Wallowsky knew this, so she's dirty, too. But Farr won't implicate Wallowsky.
Cal tells Gillian that Wallowsky is innocent. Gillian doesn't buy it; she says Cal must choose between protecting his partner -and the firm - or Wallowsky. She wants to put Wallowsky in the cube.
While Gillian tells Jenkins how to spot signs that Wallowsky is lying, Cal is coaching his lover on how to lie. So when Ria questions her, Eli's machines get nothing. Gillian thinks Wallowsky has been coached, but when Cal asks her to clear the detective's name, she walks away.
Cal tells Gillian it's all about loyalty and he would've done the same for her. "That's ironic," replies Gillian, who then tells Jenkins that Wallowsky is telling the truth.
Everyone watches Farr and Suarez get jailed. Gillian tells Wallowsky she lied out of loyalty to Cal, not her.