Detectives Jarek Wysocki and Caleb Evers respond to an armed bank robbery. They find a security guard has been shot, and the two robbers are gone. But a teller put an activated GPS device in the money bag, which Jarek and Caleb follow to an elevated train, only to discover that the robbers were one train ahead of them and have already disembarked. Jarek and Caleb then find the GPS device next to the dead body of one of the robbers.
Meanwhile, undercover officer Liam Hennessey overhears a man, Bubba, at an illegal card game bragging about his no-show construction job - his father once did Alderman Gibbons a favor - and how the Irish mob and City Hall take a cut of his paycheck. Bubba is told to shut up, then he takes a savage beating for shorting the mob on their cut. A horrified Liam tells Jarek what he's learned.
While Ernie Moosekian from the Organized Crime Unit and newly retiring officer Jonesy confront Jarek, accusing him of being too close to Superintendent Teresa Colvin, officer Rothman similarly accosts Caleb, warning that his association with Jarek will damage his career.
Jarek angrily confronts Colvin about Jonesy's exiting. But she explains that he was caught running a tow-truck scam and resigned instead of facing charges, which Jarek didn't know.
Colvin and Jarek discuss Hugh Killian, who owns Dansworth Construction, a cesspool of no-show jobs and overbilling on city contracts that they believe Gibbons orchestrated. Colvin will crack down on Dansworth's current construction site, using the O.C. unit to ticket every truck going in or out, and watch Gibbons' reaction.
Caleb identifies the dead robber as James Littleton, whose last known associates include Samuel Robbins, who just did six months in a psycho ward. Jarek and Caleb visit Littleton's last address, find that his car's hood is still warm, and call for backup. Ernie, Isaac Joiner, and Vonda Wysocki are all writing tickets when they hear this, but Ernie tells everyone to stay put.
Robbins exits the house, Jarek and Caleb move in, and Robbins starts shooting. Jarek sweeps a little girl out of the line of fire, and - with no backup - Robbins escapes. Jarek and Caleb find the stolen money, and late-arriving beat cops tell Jarek that Ernie's unit was closest to the scene and should've been there first. Jarek is furious.
Meanwhile, a staffer tells Gibbons about the construction site crackdown. When Gibbons asks Colvin about it, she notes that the site isn't located in his ward, so what's it to him? He replies that his constituents work those jobs. Once Gibbons exits, Colvin's chief of staff, Bill Hampton - forced on her by the mayor's office - volunteers to turn the heat down. Colvin says no. And when Hampton asks Colvin to keep him in the loop, she politely refuses.
Jarek and Caleb respond to a store robbery. The thief escaped, but the clerk identifies him as Robbins. Vonda arrives and apologies to Jarek, followed by Colvin, who tells him to pressure Killian.
When told of the shutdown and the serious financial losses he'll incur, Killian refuses to name any city official on the take. Jarek and Caleb then visit the hospitalized security guard, Ethel, and find that her story is full of holes.
Killian meets with Gibbons and threatens to blow the whistle if he doesn't bring Colvin under control. Killian claims that Gibbons has more to lose and demands he fix the situation. Gibbons says nothing. He then meets with Hampton, who offers to trade info on Colvin's investigations for a monthly cash payment - and a guarantee that he'll get her job when she's ousted. Gibbons gives him a handshake deal.
Jarek and Caleb visit Ethel's sister, where they learn that Ethel just lost her house, that she knows Robbins from high school, and that she was called into work yesterday. But she didn't show up to work, so they'll trace the call.
Meanwhile, Gibbons and police Lieutenant Kelly confront Killian about child pornography that Kelly found in his garage. Although Killian knows it was planted, Gibbons forces Killian to beg for his help, noting he'll keep the "evidence" to ensure Killian's continued cooperation.
Gibbons then heads to Colvin's office with Assistant U.S. District Attorney Harris in tow and plays Colvin a tape of Hampton's offer to trade info for money, which he intends to make public.
Jarek and Caleb arrive at the caller's address, order Ernie and another officer to cover the back, and head in. Robbins comes out shooting and runs for it, touching off another gun battle. As the officers close in, Robbins gets the drop on Ernie, but Jarek kills Robbins, saving Ernie's life.
Meanwhile, Colvin reacts to Gibbons' televised press conference by throwing her remote control across the room.
When Ernie apologizes to Jarek for not responding to his earlier call for backup, Jarek decks him, noting that if he had responded, they could've arrested Robbins then instead of killing him later.
Colvin then introduces Jarek to her new chief of staff, Lieutenant Kelly, adding that since Gibbons hasn't been found to be breaking any laws, he's no longer the target of any investigation. Once Kelly exits the room, Colvin tells Jarek that Kelly is a Gibbons plant who spent five years working in Gibbons' ward, so they'll continue the investigation. And - since Gibbons doesn't realize they're on to this - they'll use Kelly to funnel any information that they want to Gibbons.