The crafty 500-year-old vamp's plan was working on "The Vampire Diaries" -- everyone really and truly thought she was Elena. Nadia was holding Matt hostage to wait for the vervain to get out of his system so she could compel him to forget that he figured out Elena was really Katherine. And Katherine was wearing Stefan down, getting closer to him while pushing Damon away. Things were going her way.
Until she played her hand too far on Thursday (Feb. 27) night's episode, "No Exit," and pushed just a little too hard, and got busted. So what was her fatal mistake? Let's back up a bit.