Lucy reveals herself as a distant relative of Bonnie Bennett and turns on Katherine once she realizes Bonnie is "one of the good ones". She breaks the link and hands the moonstone to Katherine, but also incapacitates her.
Stefan and Damon orchestrate "Operation: Kill Kat" at the Lockwood Masquerade Ball. They recruit Bonnie, Jeremy, Alaric, and Caroline to help trap and assassinate Katherine. [S1E15] Masquerade
Elena discovers that her birth mother, Isobel, was Alaric Saltzman's wife and was turned into a vampire by Damon. Lucy reveals herself as a distant relative of
Katherine has a witch named Lucy cast a binding spell, linking Katherine’s physical body to Elena’s. Every injury Stefan and Damon inflict on Katherine is mirrored on Elena, forcing them to stop their attack. forcing them to stop their attack.