Overview
"The Devil Inside" is the twelfth episode of the fifth season of the American series The Vampire Diaries and the series' 101st episode overall. "The Devil Inside" originally aired on January 30, 2014, on The CW. The episode was written by Brett Matthews and Sonny Postiglione and directed by Kellie Cyrus.
Plot
The episode starts with Katherine (Nina Dobrev) in Elena's body meeting Matt (Zach Roerig). She reveals to him right away that she is in fact Katherine. She explains that she wants him to tell her everything she should know about Elena so she will be able to pretend being her without anyone noticing. She then compels him to not reveal her secret.
A little earlier that day, Nadia (Olga Fonda) worries that Elena is going to turn up and take over her body and she informs Katherine that they have to make the transfer permanent. To do that, they need her body so she chains Katherine to the bed, in case Elena takes over and escapes, and she goes to the Salvatore house to ask for Katherine's body.
Damon (Ian Somerhalder) get rids of Katherine's body and tells Stefan (Paul Wesley) that Katherine is where she should always be. Nadia shows up demanding the corpse but Damon refuses to tell her where it is so she leaves without getting what she wants. In the meantime, Elena takes over while Nadia is gone and she gets free from the chains. Before she manages to call someone, Nadia comes back and she calls Katherine back. Nadia tells her that she did not manage to take her body back and Katherine says she will go to Tyler's (Michael Trevino) welcome party and find out where Damon buried it.
From Wikipedia (CC BY-SA 4.0).