Season 4

Back from his Arizona vacation and determined to get his job back, Jack starts campaigning for being Chief of police, even though it's not an elected position. He chooses not to use the illegal taping card that might get him back in the office in no time for a future use and moves into a poor neighborhood. Meanwhile, Brander decides to go back to the force and teams up with Nancy to investigate Lester Richard's death, for which Temple got arrested. They discover that Maria ""Cashmere Brown"" Rodriguez was lying, which frees Temple – but doesn't exactly prove he didn't kill Lester vindictively.

After Chief Strickland causes the death of an innocent old lady due to having inaccurate information on the whereabouts of a dangerous drug lord, Mannion decides to catch the guy himself. He uses the help of his best men, who put their jobs at steak and work parallel to Strickland's orders. Mannion's house is burnt down after he keeps stopping kids from selling drugs. When Mannion finally catches the guy, Mayor Douglas won't give his job back, so Jack is forced to reveal that he knows the phone wire was illegal, which ultimately forces Douglas to give him his job back. Meanwhile, Temple investigates two cops whom he thinks are abusing their authority and beating the people they arrest, while Debreno sleeps with Maria Rodriguez, which causes some conflict on his friendship with Temple.

Mannion is determined to have the best people possible working for him and asks his ex-wife, Sherry, to become his Superintendent of Detectives. Meanwhile, when an ex-con is arrested for the murder of his girlfriend who was also a parolee, Mannion tries to put into action a parolee-rehabilitation program Ella had begun before she died.

Chief Mannion and his men investigate the disappearance of teenage girls who all point to a virtual suspect: a guy named Icarus who uses the internet to lure his victims and eventually murders them. The case takes a personal turn when Noland's niece becomes the next target and Joe puts all his efforts into catching the guy. Meanwhile, Temple suffers with pranks and rash commentaries from his co-workers about the death of Lester Richards, while Sherry tries to adjust to her new job.

Mannion and the team reopen a 17-year-old cold case when a girl is found murdered in the streets of D.C. ""Jupiter,"" a serial killer that was never caught, appears to have re-emerged.

Mannion investigates the death of a man during a Civil War reenactment. While Temple takes the matter personally when one of the suspects turns out to be a big time racist, it's Noland who, trying to find a connection between him and a man in an old picture, discovers a rivalry between the prime suspect and the victim that dates back to the Civil War days. Meanwhile, Debreno and Regan are out testing a new bait car that almost causes the death of a car thief.

Ricky and a friend collapse at Ricky's birthday party and are taken to the hospital, where they are diagnosed with MDMA ingestion (a.k.a. ecstasy). Mannion and his men hit the streets trying to reach the source of the drug distribution network, which leads them all the way to a man in the Netherlands. Meanwhile, Clive and Ella's sister fight over Ricky's custody, and Ricky chooses to go with his aunt to Florida. Debreno and Temple's friendship is shaken and Temple punches Debreno, still about the Lester Richards case. Brander and Cutter track down an ATM thief, a job usually done by the secret service agents – who offer Cutter a position on their staff.

Mannion searches for a modern day Robin Hood after he distributes money and stolen goods from the roof of his own building to needy neighbors on the street. Meanwhile, Temple continues to deal with the shooting of Lester Richards.

Mannion is very disappointed when he finds that the 17-year old boy who got Ella's heart is involved in a robbery of a gas station that ended in the attendant's death. Temple's day turns very sour when the mayor decides to not pick up the court fees after the Lester Richards case. Meanwhile, Nancy and her mom are attacked by car jackers, or are they?

An officer is hit by a car, and his partner is suspected of not giving him CPR, because the officer down is gay. The car in connection with the hit-and-run is traced to students performing lewd sexual acts without their victims' knowledge, then posting the videos on the internet.

A staffer is found to have hung herself because she was about to reveal names of top officials who were trading votes for sexual favors. The reporter to whom she was to reveal the news also has something of a history with Chief Mannion's family. Also, a school teacher fights for health care reforms for students and families.

People in the witness protection program become victims, and the team sets out on the case to find the killer. Meanwhile, Chief Mannion gets a specialty sandwich named after him, which then becomes ""hard to swallow.""

Mannion wants to believe that it was self-defense when his attractive fencing teacher's husband is killed at her studio. Meanwhile, Debreno recognizes a suspect in a drug case as his childhood friend who convinced Debreno to go into the Police Academy.

Mannion gets involved in a local murder investigation when he travels to a small town to fight a warrant for his arrest for a traffic violation. Meanwhile Temple and Debreno look into the disappearance of an armored truck owned by the company the Temple works for part time.

Mannion investigates the death of terminal patient afer her daughter shoots the doctor at point blank range, who she believes is responsible for her mother's death. Meanwhile Nancy must confront her own future when her father's Huntington's Disease worsens.

Mannion investigates of the murder of a young illegal immigrant leads to the discovery of a car theft ring run by a teenage gang that is selling cars as far away as El Salvador.

Mannion's determination to crack down on gangs puts Noland in the line of fire where he's shot and critically wounded.

Mannion investigates the murder of two young women, one of whom is identified as Debreno's sometime girlfriend, Maria.