Here, the official storyline of 6th episode of The Vampire Diaries Season 3:
WELCOME BACK, SENIORS — On the first day of their senior year, Elena, Caroline, Bonnie and Matt are still reeling from recent events, while Tyler seems to be enjoying everything a little too much. Damon (is annoyed by a new houseguest, and everyone is surprised by the arrival of a new student in Alaric’s history class. Matt asks Bonnie for help when he realizes he made a serious mistake. Meanwhile, Stefan continues to carry out his latest assignment from Klaus (who does not appear in the episode).