The Vampire Diaries - Season 2 Episode 4 -

Stefan is shocked that Katherine appears again to him as herself. She scares Elena, claiming she loves Stefan and wants him back. Stefan tricks Katherine, chains her and is prepared to torture her with vervain, but she proves useful and continues her story of how she tricked and betrayed the Salvatores, the Lockwoods, and hence both vampires and werewolves. Mason proves himself a dangerous adversary to Damon, and resists telling Tyler about the family curse, but finally reveals that it's triggered irreversibly by homicide. Matt is totally turned off by Caroline.