Karrens' brain has abnormalities in areas involving empathy, compassion and "an aversion to disemboweling puppies", much like a serial killer's.
Terry Karrens has slain numerous women in his "fantasies" and his uncle has been forced to cover them up.
Karrens skipped his last bail hearing, over a "minor matter" that had been resolved (since Bradley Karrens bought off the judge).
Terry Karrens kidnapped four women and paralyzed them with drugs. He referred to them as "Mother", "Little Sister", "Big Sister" and "Aunt Sheila", and posed them for a game of croquet. The drugs wore off the latter, who was able to stab Karrens with a needle, injecting him with the same drug. Karrens beat her to death, then went outside and tried to procure a new "Sheila", but in his drugged state was hit by a car, suffering brain damage.
Karrens was brought to the Dollhouse, where Bradley Karrens sought their help. However, Topher Brink discovered his brain abnormalities, and had ethical problems with reviving him. (Boyd Langton pointed this out mock-incredulously to Adelle DeWitt.)
To find out where the missing women were, Terry was scanned and imprinted into Victor. Paul interrogated him, and was making progress until Bradley left with Terry/Victor. Terry/Victor caused a car crash that killed or disabled his uncle and went in search of a new "Aunt Sheila". On Adelle's order, Topher attempted a remote wipe but only succeeded in swapping Victor's imprint with Echo's. Echo, previously imprinted as Kiki Turner in order to seduce a university professor, stabbed him.
Terry/Echo returns to his lair, just as the kidnapped women are trying to escape. He attacks one and threatens to kill them, but Echo reasserts herself and tries to get the women to kill him/her. Dollhouse agents arrive just in time.
Back at the Dollhouse, Paul is seen leaving the medical room just before Terry flatlines. Echo utters Terry's "Goodness gracious"; Terry Karens is now part of the composite Echo psyche. When Echo is later sent to the Attic, Terry's "personal hell" shows his female family members playing crochet and ignoring him (S2: "The Attic").