While responding to a call of shots fired at a family residence, Lindsay (Sophia Bush) and Halstead (Jesse Lee Soffer) discover the only survivor is the youngest daughter who is traumatized. While Lindsay and Dr. Charles (guest star Oliver Platt) evaluate the girl and see if she can help identify the killer, Antonio (Jon Seda) and Olinsky (Elias Koteas) look into a pyramid scheme "self-help" group for potential suspects. Meanwhile, Platt (Amy Morton) tries to make the case to Commander Crowley (guest star Barbara Eve Harris) for Burgess (Marina Squerciati) and Roman (Brian Geraghty) to remain partners.
When the team finds the body of a widowed, single-mother in the trunk of her car, they are shocked to discover that the victim was in constant contact with Voight's (Jason Beghe) now-reformed son, Justin (guest star Josh Segarra). After Lindsay (Sophia Bush) and Voight find Justin has been attacked in the same manor and is critically injured, Antonio (Jon Seda) and the team know that Voight will be out for revenge. Meanwhile, Roman (Brian Geraghty) makes a difficult decision and Commander Crowley (guest star Barbara Eve Harris) has plans to make changes within the unit.