After the BAU closes a case, Morgan visits one of the survivors, Daria, at a mental institution for answers to complete his report of the investigation. In a series of flashbacks, we see that the team was called to Upstate New York after three victims are found stabbed to death and displayed in various locations. JJ determines they are looking for a pair of UnSubs and Reid analyzes the wounds to find the same meticulous pattern on each body, all created by an ice pick. When Daria manages to escape her captor and is found in an amnesic state, the team has difficulty questioning her. A break in the case occurs when Daria's sister comes forward to reveal the partial license plate of the man last seen with Daria.They identify the man as Joe Bachner and learn he had an alcoholic aunt who tortured him with bee stings as a child. Joe's M.O. mirrored his childhood suffering. Daria remembers the name of the other UnSub, Coby, but the OCD nature of the crimes does not match his behavior. The team locates Joe's hideout and finds Daria's fingerprints on the ice pick. Her OCD behavior in the hospital confirms she was Joe's partner, and the team discerns that Daria was first seduced by him, then forced to participate in his killings. As a coping method, she blocked out her memory. In the present day, Daria admits to Morgan that she became a willing participant in the murders and in the next moment forgets she was Joe's partner. Knowing that she can only plead insanity at this point, Morgan breaks the news to Daria's distraught sister.