A group of detectives and officers work at the 15th Precinct, a seedy police station in Manhattan, New York City. Detective John Kelly, a 15-year veteran of the force, deals with his partner Andy Sipowitz, an alcoholic 20-year veteran detective. Laura Michaels, an aspiring lawyer and Detective Kelly's wife, is having problems with their marriage and she hires Josh Goldstein, a lawyer who lives in apartment 4B of their building to work on a divorce, who gets mugged in the laundry room of the building. Meanwhile, Sipowicz is relentlessly pursuing mobster Alfonse Giardella, who threatens Sipowicz to leave him alone. Later, Sipowicz is shot by Giardella during a tryst with a prostitute. Enraged, Kelly orders the precinct officers to hound Giardella and his ruthless employer; mafia kingpin Angelo Marino. The new patrol officer, Janice Licalsi, is attracted to Detective Kelly. But is she is revealed to be an informant for Marino who orders her to murder Kelly.

Janice's policeman father arrives for a visit and tells her about his pending indictment for corruption involving being an informant for Angelo Marino when a book that Marino had on him as a list of all of his informants... including hers. Sipowicz makes some appearances at the hotel where Giardella is staying to further intimidate him over the shooting death of Marino. Meanwhile, Kelly and Martinez are assigned a case involving the robbery and murder of a woman. Also, Josh Goldstein comes to the precinct in search for his gun he used to kill his assailant.

A minor skirmish on a basketball court leaves one of Kelly's friends dead and the other one in jail for manslaughter. Meanwhile, Sipowicz is convinced that a man knows more about his wife's death in a highway shooting than he is letting on. Laura feels as though she's being dangled in front of Giardella when Sylvia tells her to push on him harder. Janice saves Kelly's life during a drug raid and the event seems to bring them back together.

Kelly works with a Chinese detective in the investigation of the murder of an off-duty cop in Chinatown. Lt. Fancy catches Donna and Madavoy in an embrace and warns both of them about relationships in the workplace. The abused woman Sipowicz helped out turns up dead and her husband is a suspect. Meanwhile, a tough new female detective, Adrianne Lesniak, transfers into the squad because of a relationship she had with an officer at her former precinct in the Bronx and begins to work with Sipowicz on his case.

Martinez investigates a baby that was killed in a car from an apparent drive-by shooting. Meanwhile, Lois Snyder contacts Sipowicz for help because a policeman that she was entertaining died in a compromising position and he moves the body to a less conspicuous location. Lesniak's ex-boyfriend, Officer Abruzzo, keeps showing up at the precinct and harassing her, while at the same time, Lesniak locks horns with the officious Vince Gotelli over his working skills and his racy items he keeps. Kelly's future with the department is decided when Internal Affairs comes to the precinct to re-investigate some of his old cases and the result is Haverill transferring Kelly to borough dispatch duty. But Kelly decides to quit the force and after saying goodbye to Sipowitz, he throws in his badge for good.