<P> Enzo (Michael Malarkey) and Damon (Ian Somerhalder) turn people on vampires so that Damon can feed on since now, after Wes' (Rick Cosnett) injection, he craves on vampire blood and not human . The two of them try to leave the last victim's house when Wes appears with travelers who spell the house so vampires will not be able to get out . Wes informs them that he wants to make one last test; how long can Damon last before he attacks his friend to feed on . </P> <P> Katherine (Nina Dobrev), still pretending to be Elena, tries to get closer to Stefan (Paul Wesley) so they can be back together . When Caroline (Candice Accola) arrives and tells them about Damon, Stefan wants to find him and Katherine offers to go with him . Caroline warns him that it is weird for him to be so close to "Elena" after everything that happened but he reassures her that they are just friends . Before Stefan and Katherine go, Caroline gets a phone call from Tyler (Michael Trevino) who tells her that he worries about Matt (Zach Roerig), who is vanished for two days, and that Nadia (Olga Fonda) was compelling him . Katherine hears Caroline's conversation with Tyler and she calls Nadia to ask if everything is fine . When Nadia tells her that Matt found out that she is not Elena, Katherine asks her to kill him . Caroline leaves to go to Tyler's while Katherine and Stefan leave to find Damon . </P> <P> Caroline gets to Tyler's and they try to find out why Nadia would compel Matt and what does she want from him . The two of them feel awkward because of what happened between Caroline and Klaus (Joseph Morgan). At the same time, Matt tries to convince Nadia that she does not have to kill him and all he has to do is to convince his friends that he is fine . Matt returns home with Nadia and acts like everything is fine . He tells Tyler and Caroline that Nadia is not compelling him and that they just have fun together but Caroline is not really supportive of that . They both depart, leaving Matt and Nadia alone . </P> <P> Katherine and Stefan are on the road in search of Damon and Katherine tries to seduce Stefan . She breaks the car so they can stay at a hotel she had seen till the car is ready . While being there, Enzo calls Stefan to inform him about the situation he and Damon are but Katherine answers who asks him to text her the address . Stefan goes to get the car and Katherine calls Nadia to tell her that she plans to lead Stefan on killing Damon to save her . Stefan gets back and before they leave the hotel, Katherine gets closer to him and kisses him . He kisses her back but he stops because "Elena" has just broken up with Damon and it is not right . </P>

When does stefan realize katherine is in elena's body