When Lindsay (Sophia Bush) receives a panicked call from her mother Bunny (guest star Markie Post) whose boyfriend had just been shot, Lindsay must figure out the best way to approach the situation, as her mother is now a murder suspect. The case opens up when a group of high school students OD, and the drugs in question relate back to the situation with Bunny. In addition to her mother's issues, Lindsay finds herself up against the review board dealing with consequences of her actions.
After a van explodes during a Chicago street festival, a Muslim patrol officer Frank Toma (guest star Ben Youcef) goes missing and evidence quickly piles up pointing to his involvement. Burgess (Marina Squerciati) - who helped train Toma - is desperate to prove his innocence, even if that means going against her superiors.
When the team is called to an in-progress bank robbery, they come across Detective Hailey Upton (guest star Tracy Spiridakos) trying to take over the crime scene with her Robbery-Homicide unit - butting heads with Voight (Jason Beghe) in the process. As the robberies continue to be executed around the city, Lindsay (Sophia Bush) is forced to make a decision in the heat of the moment, revealing a surprising suspect behind the mask. While working on the case at the district, Upton is shocked to come across Platt (Amy Morton), who has a special connection to her past.
A live video is streamed online showcasing a tortured man being beaten and burned alive. Upon further investigation, the victim's identity is traced back to that of a man who had been previously locked up for statutory rape. When another attack of a similar nature occurs, Intelligence finds a connection between the crimes, suspected pedophiles, and group named the Perv Hunters. Meanwhile, Lindsay (Sophia Bush) runs into a few bumps in the road - both personally and professionally.