A Virginia state policeman finds a bag of body parts, while a homeless man, Todd Burton, runs through the woods scattering more parts. The  BAU's theory is that Burton is picking off hikers as they come through on the Appalachian Trail. The body parts came from seven victims, with the rate of kills accelerating. All but one are white males. Another victim, Howard Walker, is kidnapped in a nearby town. Burton attacks Lewis, and she and Alvez take him down. Burton said he was stealing food for his lost dog, Cormac. Rossi offers Reid time off to deal with his mother, who has Alzheimer's. Alvez brings his dog Roxie into the interrogation room, and Burton is afraid of the dog, which leads Alves and Prentiss to conclude that his dog is imaginary. Cormac is actually Burton's little brother, who disappeared about a year before after moving back to Dillon. Burton flashes back to his father treating the two brothers like animals, and who would make them watch as he killed their pigs. Their dad also took Cormac's dog away from him and took him up into the hills. After that, Cormac wasn't the same, and he's actually become the unsub. Todd has been trying to be his brother's keeper, cutting up the people his brother has killed. Alvez and JJ find Cormac at his father's old farm, stopping him from killing Walker. Garcia meets Roxie when Alvez is leaving, and starts to warm to him. Reid's mother misses out on a clinical trial, but Reid continues to try to find a way to help her.