When Thomas decides to stop working on active cases, Catherine starts investigating his past which leads her to an unexpected family history. Catherine takes Thomas to the basement of her step-father's house where her brother wassexually abused. Thomas tells Catherine he believes that her mother has always known about the abuse.

Thomas's suggestion to Catherine about her mother deeply disturbs her. Meanwhile, the team investigates a possible domestic homicide where a mother and her children are killed. They later find the father dead from a gunshot wound, but his time of death occurred before his family's. Thomas suspects the killer hid in the house's crawlspace, and his re-enactment affects his own family, as the killer targets another one.

After the discovery of aluminum residue on a recent victim, Catherine scans crime scene photos to see a neighboring house under construction. The foreman gives them the name of a man recently fired for looking at the neighbors. The team visits his house to find his family dead and a home video they presume he watched after killing them. They learn the general area of his current target and are able to find the exact house. Inside, the killer has cut the mother, but she opens the door for Catherine and they switch places. Catherine assumes the wife and mother role, cooks breakfast, and gets the killer to sit in front of the window at the kitchen table. He is killed by a police sniper. The situation affects both Thomas and Catherine. He promises his family to never let a case take precedence over them, and Catherine messages her mother to talk about Howard.