Katherine is back in town and no one knows her motives. She's been invited into Elena's home and now the Salvatores are working together to protect her, as it's impossible to tell what Katherine's next move with be.
Caroline's been turned into a vampire (thanks again, Katherine), causing more trouble for the bothers, not to mention all those pesky werewolves coming into town. Oh, and did we mention Klaus discovering news of the next Petrova doppelganger?