When police superintendent Teresa Colvin appears on a local radio show, an anonymous officer calls in, claiming that she's ruining the department. Before Colvin can respond, she's summoned to a multiple murder scene.
After Colvin asks her new security officer, Ray Baldwin, to determine the anonymous officer's identity, she reflects on how the 1929 St. Valentine's Massacre cost Chicago's police chief his job. When she arrives at the scene, detectives Jarek Wysocki and Caleb Evers report that three masked gunmen entered the restaurant opened fire, and escaped through the kitchen. Then Mayor McGuinness demands to see Colvin.
Colvin meets McGuinness at a photo op, where reporters fire questions about the murders and the anonymous caller. McGuinness says that he'll give Colvin the 200 new officers she's requested - and if she can't get the job done, she'll be gone.
Caleb tells Jarek that one of the victims, Paul Halland, had made reservations for seven, but only five - all of whom owned small businesses in the 'hood - arrived. Jarek wonders if they had a common vendor.
Back at the station, a police union rep discusses putting Colvin's leadership to no-confidence vote, and officers Vonda Wysocki and Isaac Joiner prepare to be deposed in an excessive force lawsuit. Jarek warns his niece that the civilian's attorney, Emma Chase, is untrustworthy.
After Caleb reports the victims' only common vendor was OG Security, one of the men who skipped the meeting says Halland thought if the owners presented a united front, they could prevent local gangleader Wayne Luckett - who owns OG Security, which is just a front for a protection racket - from running the shakedowns, adding Halland told Luckett's son about this.
Jarek relays this to Colvin, who says that Luckett is currently incarcerated, awaiting trial on another charge. But they discover Luckett is now brain dead, having suffered an aneurysm prior to the murders. Caleb notes that Luckett's gangster son, Dion, visited him before the murders. So did his straight-laced daughter, Bernadette, who is a clerk for notorious anti-police judge Locker.
When Jarek tells officers to stop criticizing Colvin, an officer accuses Jarek of having sex with her back when they were partners, and Jarek punches him. Meanwhile, Baldwin advises Colvin to not confront the anonymous officer, so she decides to ask police union president Walt Kirby's permission to address the union reps prior to their vote instead.
During Vonda and Isaac's meeting with Chase, we see the civilian's version of the events in question, wherein Isaac smashes the man's face into a mirror. Hearing this, Isaac can't control his anger, which Chase duly notes.
Jarek and Caleb question Bernadette, who denies knowing about any criminal activity - or Dion's whereabouts. But when a masked thug collects protection money from the shopkeeper who missed the meeting, Jarek and Caleb are there waiting. He runs. They catch him. It's Dion, who claims no knowledge of the murders.
When Dion learns about his father's aneurysm, he wants to speak with Bernadette. Jarek says that she already knows this, which is also news to Dion. Colvin wonders if the storekeeper said Halland's message of non-payment was delivered to his son in a typical macho assumption that a woman couldn't be a major player.
Meanwhile, we see Isaac's recollection of the events, wherein the civilian breaks the mirror while resisting arrest. Chase wants a break before deposing Vonda.
Jarek and Caleb trail Dion to an apartment where he confronts three thugs for taking orders from his sister and not him. They call for backup and arrest the quartet.
While Jarek awaits ballistic tests on guns seized in the raid that could tie them to the multiple murders, Caleb reports that there were seven cases where witnesses refused to testify against Luckett's gang. This leads Colvin to believe that Bernadette has been providing inside information to the gangbangers.
When Vonda gives her version of the events, Chase forces her to admit that she only heard, but didn't actually see Isaac subdue the civilian. Chase also wonders if Vonda's sexual relationship with Isaac is tainting her testimony.
When Colvin confronts judge Locker about the leaks, he attributes her charges to Colvin's shaky relationship with the mayor and her own force, plus his anti-police history.
Meanwhile, Jarek discovers that Dion's been released without posting bail and judge Locker approved this. But before Dion leaves the station, Bernadette arrives. She wants to keep him quiet. Dion doesn't want to obey her. Their argument turns violent, and they're both arrested.
When Colvin accuses Bernadette of everything she suspects, Bernadette puts all the blame on Dion, dismissing him as worthless.
Meanwhile, the city lawyer tells Vonda and Isaac that the case will be settled for $75,000 because Vonda's testimony contradicted Isaac's saying she was in the room. When Isaac and Vonda confront Chase afterwards, she sneers at them and drives away.
When Dion refuses to testify against Bernadette, Colvin shows him a videotape of Bernadette giving him up and dismissing his value. If Dion gives up Bernadette and the murderers, Colvin will allow Dion to take control of the gang, believing he'll quickly ruin the organization. When Dion agrees, Colvin calls a press conference to announce the murders have been solved.
Although Mayor McGuinness congratulates Colvin, he still intends to consider the results of tonight's union vote, so Colvin makes a passionate in-person appeal to the members, saying that she has their back and asking them to have hers, and avoids a no-confidence vote by a 54-46 percent margin.