Oh wow, wow, wow. Check out this synopsis from episode 21 “Isobel” courtesy of VampireSite.net. Very spoilery, so you have been warned.
ISOBEL RETURNS TO MYSTIC FALLS – Isobel (guest star Mia Kirshner) returns to town and stuns Alaric (Matt Davis) with her attitude and her demands that he arrange a meeting with Elena (Nina Dobrev.) When mother and daughter finally meet, Isobel refuses to answer most of Elena’s questions, but reveals that she will stop at nothing to find the mysterious invention Johnathan Gilbert has been searching for. Isobel’s dangerous actions lead Stefan (Paul Wesley), Damon (Ian Somerhalder) and Bonnie (Katerina Graham) to step in and help Elena deal with the situation. Candice Accola, Steven R. McQueen, Sara Canning, Zach Roerig and Michael Trevino also star. J Miller Tobin directed the episode written by Caroline Dries & Brian Young (#120)