Tyler follows his uncle Mason out on a jog. He goes down some brick steps in the woods.
Stefan and Damon recap the Lockwood weirdness: unaffected by vervane, but susceptible to the Gilbert device, plus Mason's super cool gymnastics at the carnival.
Ric thinks they might be able to get access to her notes at Duke.
Tyler follows Mason down into what can only be described as a dungeon.
If the werewolf stuff is true, Damon says: "It means Mason Lockwood is a real life Lon Chaney and that little Tyler punk may just well be Lon Chaney Jr., which means Bela Lugosi, meaning me, is totally screwed."
Matt goes to see Caroline, who can't come to the door because there's a huge patch of sunshine that blocked her path. He calls her instead. He invites her to the pool party.
At home, Elena isn't thrilled to be going to Duke with Damon to dig through her birth mother's research, but Ric will be a good buffer. Stefans staying behind because Caroline is still in danger.
The research crew piles into the car, but not before Elena sucks on Stefans face to make a point to Damon.
At the Lockwood house, Tyler asks his mom about the ruins in the woods, the old Lockwood estate the original plantation house. It burnt to the ground. He asks about the dungeon and Carol says they don't talk about it, because it had to do with slavery.
Stefan meets with Bonnie, trying to get her to help Caroline. Bonnie's not sure she can trust Caroline.
In the car, Damon tells the Elena the whole pretending to hate me is getting old. He claims he saw that Jeremy was wearing the ring before he killed him.
Bonnie explains the ring rules to Caroline, including that she will de-spell it if Caroline kills anyone. Bonnie lets sunlight hit the ring, shuts her eyes and announces she's done.
She throws open the curtain, bathing Caroline in sunlight to prove that it works.
At Duke, Alaric introduces himself to Vanessa Monroe, a research assistant and Isabelle's former student. She lets them into Isabelle's office. After a moment, Damon notices that Vanessa is gone. She comes back in with a crossbow, aimed at Elena.
Damon darts over and stands in front of her and is impaled on the arrow. Damon grabs Vanessa.
Later, Elena yanks the arrow out of Damons back. He wants to kill Vanessa, but Elena tells him not to. She threatens to never speak to him again.
Vanessa freaks out to Ric, explaining that it's not possible for Katherine Pierce and Damon Salvatore are alive. She read that he died in 1864 in Isabelle's research.
Elena explains shes Isabelles daughter and Katherine's descendant. And Damon is Damon.
In the woods, Stefan tries to teach Caroline how to feed on rabbits. She freaks out a little, which entertains Stefan. He explains that when someone becomes a vampire their personality is amplified. When he was human he cared a lot about people and felt bad if he hurt them.
"So you're saying that now Im basically an insecure, neurotic control freak, on crack?", she asks.
Stefan agrees that if they hunt first, hell let her go to the swimming hole for Tyler's party.
Mason drives by the party and tells Tyler to have everyone out of there by dark. He says its because the family is liable if something happens.
He glares at Stefan at he leaves.
Caroline finds Amy flirting with Matt. She compels Amy to leave to find a single guy to flirt with, which prompts Matt to give her grief for showing up and being the jealous girlfriend. When Matt leaves, Stefan tells her not to compel people for petty stuff. She's not thrilled her jealousy is also amplified.
At Duke, Vanessa helps them go through Isabelle's thing and finds an Aztec legend about vampires being cursed by a Shaman to be slaves to the sun and werewolves slaves to the moon, dating back 600 years.
When the full moon crests to the sky, the werewolf-cursed turn. Instinct compels them to hunt vampires. Damon thinks he would have heard about it, but Vanessa explains werewolves were almost hunted to extinction by vampires. A werewolf bite is fatal to vampires.
Night falls at the watering hold and the party packs up. Caroline goes to talk to Matt as Elena calls Stefan. Its a full moon.
Caroline promises Matt no more drama and they go off into the woods. Elena warns Stefan. He looks over and saw Caroline was gone.
He calls her but shes left her phone behind.
Mason Lockwood locks himself with chains in the dungeon. He puts something in water and mixes it. He hears voices approaching. It's Tyler taking Amy down to the dungeon.
She checks that he is single and goes with him.
Back in the woods, Mason looks for a tree to chain himself to. He climbs in his SUV, which shakes as he screams inside. We hear growls.
At Duke, Elena asks Vanessa what she knows about Katherine. All she had was a photo. She says doppelgangers usually torment their doubles. Damon infers he knows something about it, but won't say.
In the dungeon, Amy no longer feels compelled to make out with Tyler, says she likes Matt and leaves.
Stefan finds Mason's SUV. He sees the unhooked chains. He sees the yellow eyes inside. A wolf leaps out at him and runs off into the night.
At Duke, Ric checks that Vanessa won't talk. She's intrigued. Ric says Isabelle became her research: she became a vampire.
At the car, Damon gives Elena a book at that says Petrova. Katherine's real name was revealed as Katerina Petrova and she was from Europe.
Damon points out to Elena that she hated him before and yet they became friends after. It would suck if that was gone forever, he says. He asks if thats gone forever and she only thanks him for the book.
In the woods, Caroline and Matt start to kiss. He hears a growl, but shes too vamp-horny to care. He accidentally cuts himself on a branch and draws blood. She kisses it at first, then more. He's getting totally creeped out when she chomps down and then bites his neck. He sees her fangs, but she's too into it to care.
Suddenly Stefan comes out of nowhere and pulls her off. Mason the wolf is on the prowl. Stefan compels Matt to stay down and tells Caroline that they have to run for it to draw it away from Matt.
They're running when they come upon Tyler. He asks them what theyre doing there, when Mason the werewolf comes out of nowhere and jumps on Caroline. Stefan tackles it and knocks it off. Its about to bite Stefan when Tyler commands it to stop.
Mason the wolf runs off.
Later, Caroline compels Matt, to tell him an animal bit him.
Stefan dealt with Tyler and says they'll put Matt on vervane, which will mean she cant compel him or drink his blood.
She asks if she should walk away form Matt. He says he knows he should have walked away from Elena, but he can't.
Tyler finds his uncle's SUV in the woods and his shredded clothes inside. His naked, muddy uncle comes up behind him and asks for his pants.
"It was you", Tyler says. Mason nods.
Caroline goes to meet Matt, but Amy sits down with him as she walked in. Caroline takes a deep breath, gathers herself, and then goes over and puts on a good jealous act for them. It works, he breaks up with her.
Ric comes back to Elena's house and finds Aunt Jenna and he kisses her.
Outside, Damon thinks he's chipped a little off Elena's wall of hatred. She asks him for the truth, if he knew Jeremy was wearing the ring. Damon admitted that he didn't. He says Katherine pissed him off and he snapped. He apologizes. She tells him the answer to whether he's lost her forever. And it was a yes.
"But you knew that already", he realizes, "you used me today."
She wanted information about Katherine.
"You and Katherine have a lot more in common than just your looks", he says and walked away.
The next morning, Caroline wakes up with Katherine standing over her. "Don't be frightened, were going to have so much fun together", she says.
p recap Memory Lane
Stefan takes drastic measures to find out the real reason Katherine has returned to Mystic Falls, and is shocked when she reveals new secrets about what really happened in 1864. Damon tries a new tactic to resolve his issues with Mason, but it proves costly. Tyler pushes Mason to tell him the truth about the Lockwoods. Finally, when Katherine delivers an ultimatum, Stefan and Elena are left with very few options.