At Charlie's house, Charlie and Amita learn from Alan Eppes (Judd Hirsch), Don and Charlie's father, that a MIT professor had asked NASA to look into Larry's recent behavior. As a result of Larry's homelessness, NASA decided to pull Larry from the mission. FBI Special Agent David Sinclair (Alimi Ballard) and Colby Granger (Dylan Bruno) take Brendan McCrary (George Newbern), a frequent visitor in the chat room that the molesters used, into custody. When the team questions McCrary, they learn, and further investigation confirms, that McCrary joined an online group which attempts to peacefully catch child molesters after his daughter, Katie, was raped and murdered by one, and he has an alibi for two of the murders. While working on their model, Charlie tells Amita that he feels bad for being happy that Larry was not going to space, and Amita tells Charlie that he should not beat himself up over his emotions. Their analysis soon reveals that the killer's preferred houses are located in Megan's Law and Jessica's Law zones. David finds online videos of the molesters' confessions taped just before their murders. While attempting to trace the source of the videos, Charlie finds one uploading as the agents discuss the case and uses onion routing to trace the live feed. Unknown to Charlie, the killer piggybacked the system, causing Charlie to send the agents to an address two blocks from the site of the latest murder. Later, Charlie suggests using the syntax of the chats to determine if McCrary or any of his relatives, who would have similar syntax to McCrary, could have contacted the victims. Meanwhile, Larry expresses his disappointment about the mission to Megan, and Megan asks Charlie to help Larry fulfill his dream. While Megan brings the files containing the chats to Charlie, she and Amita overhear Charlie vouching for Larry to someone at the NSA. Larry later thanks Charlie for persuading NASA officials to allow Larry to be on the mission. Using the information from Charlie's analysis, Don visits the McCrary family. He learns that McCrary's son Matt (Johnny Simmons) thought that his family was not doing enough to stop molesters after what happened to his sister, so Matt contacted someone in an online support group for families affected by sexual predators to discuss non-violent ways of vengeance. He also gave them the names and contact information of predators that his father was investigating, but he swears that he didn't know they were going to be tortured and killed and is horrified that he was an accessory to murder.