The BAU is called into help the local authorities in Cherry Creek, Colorado after a series of brutal home invasion murders. Quickly the team recognizes two different signatures, fitting two distinct personalities. The first man kills the parents violently, while the other drugs the children like an "angel of mercy" murderer. But the two men come under a microscope when one of their victims survives an attack. The girl, Carrie, now an orphan, says the men call each other "brother," despite the fact that they are of different races.
After the team realizes the type of drugs used to kill the young children come from a pet euthanization facility, one of the men, Ervin, is identified. He and his "brother" grew up in foster care, and initially pursued the families who abused their foster children. Eventually, that wasn't enough, and they began to kill others. Ervin wanted to stop, but Gary had been abused in far worse ways, and his killings were merely rehearsals for the way he wanted to kill his destructive foster mother. Gary kidnaps a child from his mother's foster home and nearly convinces him to murder the mother, but Morgan talks the young boy out of it. Gary and Ervin go down for the killings. Prentiss is deeply affected by the story of Carrie, the girl who helped them solve the case. She wants to bring her home, but Carrie is sent to live with her cousins in Los Angeles. Though Prentiss knows it's the right thing, she can't help but wonder what it might have been like.