The BAU is called to investigate after two skeletons are uncovered in a yard after a water main burst.  When Hotch confronts the owners and their son Lyle, Lyle takes off running. Hotch catches him and all three family members are taken in for questioning.  Meanwhile Blake and Reid remain at the scene, where they eventually discover two more bodies, this time men. The medical examiner determines that all of the bodies were sexually mutilated.  Lyle at first admits to killing the women, but the BAU realizes he's making a false confession. They then turn their focus to Charles, Lyle's dad. It turns out that back in high school, he was the victim of a lynching, based upon a false accusation of rape by a girl who got home from a party after curfew. The girl's brother is a member of a KKK chapter, so he and his KKK friends hunted Charles down and castrated him. Years later, the girl wrote Charles a letter, apologizing for ruining his life, and this flipped his switch.  He began hunting down the people who lynched him and, in cases where they had already died before he could get to them, he murdered their daughters.