Det. Casey Shraeger was working in vice until a fellow officer is murdered. She is quickly moved to homicide to help investigate the murder, and find out if he was crooked or not. Casey begins to find out some interesting facts about her new co-workers.
A family of criminals has the detectives running all over the city until Walsh and Shraeger discover their motives and negotiate a stop to all the crime. Brown has Shraeger investigate Walsh's past because her former partner turned out to be a dirty cop. Meanwhile, Cole's former partner in crime returns, making it even more difficult for Cole to continue to hide his criminal past.
Detectives set up a sting at a store that deals in murder weapons and body-disposal advice. Elsewhere, Shraeger is asked to get someone out of a resisting-arrest charge, and Frank Lutz has bad timing when he asks Cole for a favor.
When Beaumont is in a pawn shop to get some cash the shop is robbed by a man and a woman. The woman is later the target of Shraeger and Walsh's investigation when she robs a bridal store with a different man.
Lutz pulls a gun at Walsh's diner, striking Beaumont. While investigating, Walsh and Shraeger begin to discover Lutz and Cole's past connection. Elsewhere, Banks and Delahoy track a string of bus robberies, getting help from a clairvoyant passenger.
Walsh and Shraeger try to help Off. Powell, who fears he may have killed someone during an alcohol-induced blackout. Meanwhile, becoming victims of identity theft inspires Banks and Delahoy to make some changes in their lives.
When George Reed, a wealthy business man receives a death threat, Casey and Walsh are assigned to protect him. A disturbance draws Casey and Walsh away from their post and they return to find Reed gone and his room ransacked. Later they receive a ransom call demanding $10 million for his safe return. Banks and Delahoy are assigned to a case involving an 87 year old man on a crime spree.
Alvarez takes over while Sergeant Brown is away. Things go south when Alvarez releases Bo Keebler, a man who recently tried to rob a Chinese restaurant, into the custody of U.S. Marshall Foster. Casey Alvarez, and Walsh discover information that suggests Foster isn't exactly who he claims to be after the precinct receives a bomb threat. Banks tries to stay in his apartment until after his 43rd birthday to keep from being killed.
When a drug store owner is shot while running down the street naked, Walsh and Shraeger investigate. Information from the boyfriend of the victim's daughter leads the detectives to a loan shark that the victim had an argument with a few nights earlier. After a series of tapes from an apology line service turn up missing Beaumont and Cole look into the theft. Meanwhile Delahoy convinces the medical examiner to give him an MRI, and he receives some unexpected news.
Beaumont and Cole interview a couple after their apartment is broken into. When nothing turns up missing the couple discovers that an adult film they rented was filmed in their apartment. The film leads Delahoy and Banks to a series of bizarre adult films shot in several local apartments. Cole investigates a link between all of the tenants. In an effort to solve the case Beaumont and Cole go undercover and try attract the film maker for another movie. Scraeger finds herself emotionally invested when she takes a 10 year old case involving a violent attack.