Instead, she wants a meeting with Elena, and she threatens to kill Alaric's students if this doesn't happen. Alaric informs Elena, Damon and Stefan that Isobel is back and the meeting is arranged; it ends up breaking Elena's heart. Her birth mother is as cold as it gets, simply demanding that Elena hand over John Gilbert's invention or she'll hurt the ones Elena loves.
Later, when Damon confronts Isobel over her threat, she says that Katherine is behind all this, but Damon doesn't fall for it. He says that "bitch" can come to town herself if she has any business there.
We also learn just what the invention does, thanks to Bonnie who tries to make up with Elena by going through Emily's spell book with her. Turns out, John Gilbert never really invented anything. Emily simply cast witch spells on his devices so he would think they were his doing. The one in question now? It can be used as a weapon AGAINST vampires.
So, why would Isobel want it? John admits to Jeremy it's so she can prevent a dangerous group of vampires (from the tomb) from taking over Mystic Falls.
A plan is hatched: Bonnie says she can reverse her ancestor's spell, so when Elena hands the invention over to Isobel and John, it won't work - but they won't know it. This is what takes place. The exchange is made. Elena tries to be strong when Isobel once again proves how she doesn't care about her daughter, and also gives her the warning to get away from the Salvatores. Isobel also mentions an observation she's made: Damon is in love with Elena.
Stefan later confronts Damon about this, and the latter says he won't pursue Elena, but he says so with the typical Damon grin.
Isobel also confronts Alaric to say goodbye and compels him to get over her. A nice gesture, really.
So that's where we stand as the episode comes to an end, until a pair of twists:
- Bonnie admits to Caroline, without telling her any specifics, that she claimed to have done something for Elena, but she lied. Translation: the weapon, which Isobel has dropped back off at John's CAN kill vampires.
- Damon's theory, which he shared with Stefan, is correct: on a phone call from Isobel confirms that John is actually Elena's father, and Isobel has Elena's best interests in mind. She says John must go through with the plan to kill all vampires, including Damon and Stefan, because she's their daughter and they don't want her growing up around blood suckers. They owe her that much, Isobel says.
Source: TV Fanatic