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.

Inspector Lastarza of the Organized Crime Unit tells Lt. Fancy and Kelly that they stop applying pressure to the local mob for their pursuit of Angelo Marino is hurting the FBI investigation to nail Marino. Meanwhile, Sipowicz regains consciousness in the hospital after the shooting, but he has no memory about the attempt on his life because he was drunk at the time. Laura and John Kelly become officially separated and she decides to join a private law firm. Josh "4B" Goldstein becomes more paranoid about his mugging and brings a gun into the laundry room every night in hopes to catch his attacker. Kelly tries to reason with a deranged man who has taken a judge hostage who let his son's killer free. Elsewhere, Angelo Marino puts more pressure on Janice to murder Kelly, but she kills him and his chauffeur/bodyguard instead and slips away.

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.

Martinez goes to visit his drug-addicted brother, but finds the superintendent of his building, Hanlan, is a retired cop who is on the take and is forcing the tenants out, and Kelly sets out to prove that Hanlan is responsible for the death of two of the apartment's residents. Meanwhile, Laura's new job as an Assistant District Attorney takes a turn when she's assigned to a case that involves Giardella. Also, the squad deals with Detective Stillwell, a prankster whose jokes in the station house get out of hand.

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.

A shady homeless man, named Lou, comes to the station thinking he's a werewolf and demands to be locked up into a cell before he kills someone when the night comes. However, things take a turn when Kelly investigates Lou when he may be a witness in the murder of a nine-year-old immigrant boy. Meanwhile, Sipowicz is visited by his long-estranged son, Andy Sipowicz, Jr. with his fiancée, Patty Constance, an older woman who Sipowicz discovers that she has been cheating on Andy Jr. Elsewhere, Giardella is killed in his hotel room by a Mafia button man dressed as a window washer before he can testify to a grand jury against his superiors and Laura finds herself the only witness to the murder.