A major subplot involves regression. This episode marks a dark turning point for his character. Vampire Diaries, Season 5, Episode 12: The Devil Inside
The episode hinges on dual performance. For the first time, the conflict is internal; Elena is trapped within her own mind while Katherine pilots her life. Watch The Vampire Diaries S05E12 HDTV XviD-AFG ...
Katherine uses her knowledge of Elena's history to manipulate those closest to her. She even compels Matt Donovan to act as a "crash course" on Elena’s recent life to ensure her performance is flawless. A major subplot involves regression