When an anonymous caller says that a bomb will explode at the Bix Biomedical building in 15 minutes, detectives Jarek Wysocki and Caleb Evers rush to the scene. As the bomb squad pinpoints the eight sticks of dynamite and police begin to clear the area, Jarek pulls a pedestrian to safety, then BOOM!
Meanwhile, Alderman Ronin Gibbons reminisces about why he entered politics in 1981: his father had received an erroneous and overinflated tax bill. He also remembers the members of his community who made him successful, which is why he's pressing the flesh by getting his haircut at a local barbershop. When an armed teenager attempts to rob the place, Gibbons fires a concealed pistol, hitting him in the leg, and calls for the police as well as an ambulance.
While Gibbons' aide tells reporters the alderman is authorized to carry a concealed weapon and Gibbons promises to pay the gunman's medical bills, the bomb squad disarms another explosive device at a karaoke bar. Caleb theorizes that these bombs share a historical connection.
As Gibbons remembers growing up in Chicago's Cabrini-Green projects, he visits the wounded gunman, Blake, at the hospital and asks who made him the triggerman. No answer. When Blake's mother claims that he's no gangbanger, he's just confused since he lost his grandfather a few months back, Gibbons says don't worry, he'll protect Blake.
Jarek tells police superintendent Teresa Colvin that the Chicago Liberation Army killed three civilians with the same type of bombs back in the '70s, when the karaoke bar was a U.S. Army recruiting office, adding that CLA leader David Argyle was never prosecuted. Argyle became a California college professor and just returned to Chicago to pick up an award.
Jarek and Caleb find Argyle at a book signing, where a man throws blood on him. They subdue the attacker - his father was killed in the '70s bombing, which he claims Argyle planned - and arrest Argyle as well. Argyle denies being involved with any past or present bombings.
Colvin shows Jarek security video footage of Gibbons in the barbershop, noting that Blake didn't take any money. That's because it wasn't a robbery: it was an attempted hit. But Gibbons isn't filing charges because he wants to cover up something. Colvin wants to know what.
As Gibbons continues to reminisce about Cabrini-Green's decline and how he became determined to see it demolished, he tells Blake and his mother that all charges will be dropped. He gives Blake a high-def TV and video-game system, and he gets a handshake of friendship in return.
Jarek and Caleb tail Argyle to the Chamber of Commerce building, where they find him bloodied with an identical bomb by his side. Argyle says he was attacked from behind, but in an attempt to help them -and with his lawyer present - he admits the Board of Trade Center and the Daley Building were the other original '70s targets.
Meanwhile, Colvin meets with undercover cop Liam Hennessey, who says that the black gangs in Gibbons' ward don't get the protection that the Irish mob does and alderman's death would change that. Colvin relays this info to Jarek, adding that they need to determine who ordered the hit before Gibbons does.
Jarek and Caleb discover that former CLA member Linus Westermeyer, who cut a deal and was never jailed, still lives in Chicago. When they raid Westermeyer's home, they find the CLA's signature bomb-making materials. Caleb notices eight sticks of dynamite are missing, indicating another bombing is coming.
Westermeyer says Trey Stein - the son of CLA members who was born while they attempted to avoid being captured (his father died awaiting trial; his mother's now serving 30 years) - had been living in his basement. Trey blames Argyle for ruining his family's life. He also left an hour before the raid, taking a backpack with him.
Jarek, Caleb, and Colvin race to Argyle's hotel. Snaking a video camera into Argyle's room, they find him bound with the dynamite strapped to him. There's no timer on the bomb, which means the detonator must be physically connected, so Jarek, with Colvin relaying what she sees on camera, enters the room.
Meanwhile, Gibbons plays video games with Blake and persuades him to name the person who ordered the hit: "Little Monster" of the Southside Mafia.
When Jarek finds Trey holding the detonator in Argyle's room, he asks Colvin to provide a phone link to Trey's mother - whom Trey believes is an innocent pacifist - from prison. As Trey's mother orders him to take revenge against Argyle, Caleb sneaks into the room, and subdues Trey from behind.
Colvin and Jarek then confront Blake's mother, who refuses to cooperate, which indicates Blake's already cut a deal with Gibbons. Meanwhile, Gibbons' aide meets Little Monster, who says that Blake was only supposed to wound Gibbons as a warning; he just wants the same protection and split that the Irish mob enjoys. When Gibbons hears this, he and his aide - who told Little Monster they have an understanding - laugh uproariously.
Across town, Jarek and Caleb find Argyle addressing the crowd at his awards dinner and arrest him for conspiracy to commit murder in connection with those '70s bombings. (He'd implicated himself with a lawyer present.)
As Gibbons, his aide, and Blake watch news reports - complete with Gibbons' self-satisfied speechifying - about the last remaining building in Cabrini-Green being demolished, beat cops find the body of Little Monster.