The record-breaking summer heat and the likelihood of blackouts send the Chicago Police Department into the streets in full force to temper the city's escalating violence. Alongside her new driver, Superintendent Teresa Colvin finds herself back in the field while Detectives Wysocki and Evers take over an emotional case in which a son witnessed his father's fatal shooting. Meanwhile, Alderman Gibbons enlists Liam to help keep his constituents cool.

When five merchants are gunned down in a restaurant in Lincoln Park, relentless press coverage prompts the embattled mayor to blame the city's rising crime problem on Superintendent Colvin, who, in turn, unleashes Jarek and Caleb to catch the killers in hopes of restoring her credibility as a competent leader. Meanwhile, Isaac and Vonda are forced to revisit a past domestic violence case.

While Teresa and Jarek set the stage for their case against Alderman Gibbons, their effort to clean up Chicago takes an unexpected turn when a deadlocked jury acquits a corrupt city official. Suspicious, the two mount an investigation, only to discover that jury tampering is just the tip of the iceberg.