Plot

As Damon's behavior escalates from destructive to deadly, Stefan begins to regret their last conversation and decides to track Damon down and intervene. For reasons of her own, "Elena" volunteers to come along. Dr. Wes enlists the Travelers to set a trap that will once again test Damon's friendship with Enzo. After a heart-to-heart talk with Nadia, Matt enlists Caroline and Tyler's help to protect Elena, leading to a violent confrontation. Later, when Stefan tries to comfort a dejected Caroline, their conversation leads to a horrifying realization.

Enzo helps Ripper-virus-infected Damon creating vampires to feed on to their death. Wes uses the Travellers magic to lock the buddies up, determined to force Damon to turn on Enzo, who is however dart-injected just in time. Tyler worries about Matt's long absence and informs Caroline that he suspects Nadia of compelling, in fact combined with making out. She eagerly comes, hoping to make up, but when Matt is returned unharmed, against Katherine's cruel advice, the only result is a fight during which hybrid Tyler bites Nadia, who fears that's fatal. Dreaming of eternal love with Stefan as Elena, Katherine resolves to trick him into killing Damon to save her on a rescue mission. Stefan not only finds a non-lethal alternative, but also starts suspecting it's not really Elena.—KGF Vissers

In a farm house, Damon and Enzo wait for the farmer to come back to life. Now that Damon has to feed on vampires, they're turning people so he can feed on them.

Enzo is staying, saying he doesn't abandon his friends. Plus, if Damon hadn't gone with him to kill Dr. Wes, Damon wouldn't have been turned into a vampire killer. When the farmer wakes up, they feed him blood so he'll turn. Then Damon rips his head off.

At the Salvatore house, Stefan quizzes Katherine-in-Elena on dates in history. She knows a little too much about the Holy Roman Empire, which Katherine lived through. Stefan takes note. She quickly tries to cover, saying she did a paper on it in high school.

Caroline comes by with police reports from her mom. Katherine is annoyed to have her alone time with Stefan interrupted.

The police reports show a string of people found inside their own homes with their heads ripped off and skin desiccated. Stefan realizes it means Damon is feeding on vampires.

Stefan tries to blame himself, but Caroline won't allow it. Caroline is surprised to see Elena there, and doesn't buy her excuse that Stefan -- who doesn't go to college -- was helping her study.

Tyler calls Caroline. They haven't spoken since, as Stefan puts it, Tyler tried to kill her. Katherine overhears as Tyler asks about Matt and tells her Nadia was compelling him and now he hasn't been home or to work. Stefan seems to see Katherine/Elena alarmed as she listens in. Caroline insists on coming over to Tyler's.

Elena leaves and Caroline worries about whatever is going on with her, pointing out she went from planning to fight for Damon to dumping him to spending time with Stefan. Stefan is confident that he'll figure out whatever's going on with her on their trip to find Damon.

Back at Whitmore, Katherine calls Nadia. When Nadia tells her that Matt knows about her, Katherine insists Nadia kill him. But Nadia has been keeping him hidden until the vervane is out of his system so she can re-compel him.

Katherine tells Nadia to deal with Matt before she gets back in town or she'll do it. When Nadia gets off the phone he promises her he can convince his friends he's OK.

Damon and Enzo prepare to leave the farmhouse for New York when Damon hears the telltale chanting of Travelers outside. They open the door and find they are stuck inside -- and Wes Maxfield is there. Damon is his patient zero and he wants to see how long Damon can go before he feeds on his best friend. They're trapped.

Stefan and Elena stop for gas. He notices that she seems to have written Damon off in a way she hasn't before and Katherine tries to play it off as just wanting off the Damon redemption rollercoaster. She sends him inside for food then sabotages his engine.

At the farmhouse, Enzo knows Damon can go eight hours without feeding. Damon doesn't want to call Stefan after he told him to leave and not come back. Enzo thinks Damon is willing to risk him, but not his friends. Damon assures him he's not going to feed on him.

At Tyler's house, they get past the awkward silence and start to talk about Matt, when he walks in the door, followed by Nadia. He says he was with her, then invites her in.

Back at the gas station, Stefan finds the piece of his car Katherine ripped out. He asks her to hold the part, noting it has grease on it. When he's looking into the engine, she rubs grease all over herself. Then she cutely suggests they get a room at nearby hotel to shower and change. He tries to insist on staying with his car while it gets fixed, but she convinces him to join her.

Back at Tyler's house, Matt spins a yarn about being on the way out of town but finding Nadia waiting for him on his front steps. She tells Tyler she feels bad about snapping his neck. Matt says he lost his phone and they were in Atlantic City, but Caroline isn't buying it.

She tries to compel Matt to tell the truth, but he gives the same answer with his vervane bracelet on.

Nadia turns on Caroline for being judgmental over Matt's romantic choices given her own. She tries to draw Tyler into it, but he leaves.

Caroline follows Tyler, not able to believe he's buying their story. "It's a hell of a lot easier to buy than other things that have happened," Tyler says as he walks out the door.

At the motel, Stefan tells Elena (Katherine) that he understands what Damon is going through because he was in love with her once and lost her. He doesn't think Damon is handling it properly, but he sympathizes. Katherine brushes his hand with hers but he goes to change.

Back at the farmhouse, Enzo chains Damon to a chair (with his permission). Then Enzo calls for back-up. "I told you your pride isn't worth either of our lives," Enzo says to Damon's objections.

He calls Stefan, but Stefan isn't near his phone and Katherine answers. Enzo catches her up to speed as Damon shouts in the background for them not to come. Katherine tells him to text her the address and they'll be on their way. He tells her he's under strict orders to kill Damon if he tries to feed on her. He's kidding but it gives her an idea. She doesn't tell Stefan about the call.

At the farmhouse, Damon is worried he'll feed on them if they come. Suddenly, there's a shot. Wes shot Enzo in the shoulder to see if Damon would get hungry enough at the smell of his blood to break the chains.

Damon busts through easily and attacks Enzo. Enzo tries to remain calm and yells at Damon to stop. Finally, Damon pulls off and starts wretching.

Wes tells him the Travelers raised the acidity of his blood so Damon was essentially drinking hydrochloric acid. He'll allow Enzo to leave because he wants something from him. At first, Enzo insists on staying, but Damon tells him he tried to kill him once and he'll do it again. He yells at Enzo to leave and he finally does.

Back in the motel room, Stefan gets word that his car is fixed. Katherine showers and does everything she can to tempt Stefan, including leaving the door open when she gets dressed. She walks over to him with dripping wet hair and presses up against him. She kisses him. He tries to resist and finally breaks away, saying it's wrong because she just split up with Damon.

She apologizes and suggests he settle the bill while she finishes packing. When he leaves, she enjoys her first victory.

She calls Nadia, wondering who Stefan loves more: Elena or Damon. She wants to make Damon attack her so that Stefan has to kill him to save her.

When Nadia gets off the phone, Matt tells her she's an idiot if she thinks Katherine will choose her. He knows what it's like to have a mom who only cares when it was convenient. Nadia brushes him off, adding that he's just trying to save Elena.

She bites his wrist and announces the vervane is gone. He kisses her, since he's going to forget it anyway. He thanks her. "If I'm going to be threatened and held against my will I can think of worse scenarios," he says.

She wants more and kisses him. He rolls on top of her and takes out a phone. He sends a text. He gets as far as "Help. K-" when she sees.

She's upset and feels betrayed by him. He tells her she's not like her mom, she compels him to forget everything. She gets up to leave but runs into Caroline at the front door.

Matt sent a text to her from Nadia's phone, but now has no memory of it. Caroline sees he was compelled again and attacks Nadia.

Nadia gets the better of her. Nadia tells Matt that he may not remember, but this is all his fault. She's about to attack Caroline when Tyler races through the door. He announces that young hybrid beats old vampire and wrestles with her, but she gets free and runs off. Matt looks for an explanation.

In the farmhouse, Katherine and Stefan arrive. He warns them not to come in. Stefan says he's not afraid of him. Katherine calculates then steps into the farmhouse, which she can't leave due to the Travelers' spell.

She tells Damon she's proving to him that he's not a lost cause. Stefan follows her in. She picks up a shard of ceramic and cuts her hand, tempting him, saying his love for her is stronger than his craving.

Damon vamps out and tries to resist, but shouts at her to get away. She toys with him in the guise of being helpful. Stefan tries to stop her, but she tells him Damon will be OK.

She pushes her bleeding hand in Damon's face until finally he can't resist anymore. He chomps down on her neck.

Katherine waits for Stefan to save her. As Damon gnaws away, she even kicks a handy stake closer to Stefan's feet.

But Stefan doesn't want to hurt Damon. Instead he picks up a shard of glass and cuts his own arm, tempting Damon away from Katherine. Then he snaps Damon's neck.

Back at Tyler's house, Caroline reports to Tyler that the only thing Matt remembers is he slept with Nadia (the cover story she gave him).

She turns to go, but Tyler stops her to apologize. She tells him she wants things to be good, but he reminds her she slept with the guy who killed his mom, so they're not going to be good.

Damon wakes up chained in his own cellar. He tells Stefan he's stupid for bringing him home and eventually he'll kill him. But Stefan reminds Damon he's his brother and won't give up on him.

Damon thinks Elena has. She knew what being an Augustine vampire meant for Damon. She had to kill Jesse when he was one because it was the only way. And Damon saw her kick Stefan a stake.

"Are you saying Elena wanted me to kill you?" Stefan asks. "You got another excuse?"

Stefan thinks about it and leaves.

Katherine joins Nadia in a diner. She giddily tells Nadia that she had a moment with Stefan. Nadia is disappointed that it's all Katherine cares about.

"I'm in a really good mood right now, which means I don't want to have to worry about whatever's making you mopey," Katherine says.

"You won't have to worry about me much longer," Nadia says. "Tyler Lockwood bit me."

Nadia reveals a bite on her arm.

Back at the Salvatore house, Caroline shows Stefan her "Help. K" text from Matt. Stefan tells Caroline that Elena (Katherine) is acting strange and kissed him.

Caroline doesn't understand, and knows that would destroy Damon.

He tells her Damon's theory, but Caroline doesn't think Elena would ever want Damon dead.

"Unless... Matt texted you 'Help. K' before Nadia stopped him. K. As in Katherine," he says. He remembers Nadia trying to transfer Katherine's spirit to her as she was dying.

"But that didn't happen because Katherine had a change of heart," Caroline says.

Then they both realize what actually happened.

"It's Elena, we know her! Oh my god," Caroline says.