THE VAMPIRE DIARIES Season 2 Episode 4 : Memory Lane
Katherine tells Stefan that she will kill Elena unless he ends his relationship with her. After Caroline tries to break up Elena and Stefan, Elena realizes that Caroline is working for Katherine. Elena and Katherine finally meet, but Katherine ignores Elena's questions. Damon stabs Mason with a silver knife, which backfires when Mason says that silver hurting werewolves is only a myth and they are now enemies. Katherine remembers what happened in 1864, after Stefan and Damon were shot in an attempt to save her. She had kissed Stefan, declaring her love and saying they would be together again one day. Stefan and Elena stage a fake break-up to prevent Katherine from hurting anybody.