Okay, so I think this was my favorite episode of the season so far.
Elena, worried that Damon hasn't gotten in touch with her, goes to see Aaron to ask if he knows where Wes might be. He brings her to the Whitmore House. She's concerned since this is a residence and she probably won't be able to enter, but he invites her in and it works. Turns out, he owns pretty much the whole college. His parents left it to him when they died. Wes comes down the stairs and pretty much immediately injects Elena with vervain.
Aaron is freaking out and confused. But Wes tells him about vampires. He dumps Elena down in the basement in a cell next to Damon and heads back upstairs to lay out the truth to Aaron.
In the basement, Elena finally wakes up and is very confused (understandably). Damon explains to her that he's been here before. And he launches into a flashback to 1953 when he was last in this cell. He was trapped there for five years before he managed to escape. However, when Elena presses him for details of the escape, he's vague and doesn't really want to answer.
Instead, he tells her about the friend he made, Enzo. Enzo had been trapped there for 10 years before Damon got there. Enzo helped him hold on to his sanity while the two of them were mercilessly tortured. They would yank out their eyes, and put off parts of their organs to watch them regenerate. And just generally be a bunch of fucking assholes. He and Enzo helped pass the time by imagining what they were going to do to the doctors when they got free. And Damon claimed he was going to kill the entirety of the man's family.
Eventually, Elena persuades him to tell her how he actually escaped. Once a year, on New Year's Eve, they brought the vampires up to the party to show off the research they were doing (and how effective vampire blood was at healing). But they were so weak (they were only given a tiny cup of blood a day to keep them alive) they couldn't fight back. Enzo thought it might be a good idea for one of them to drink both cups for the whole year. Then, when they went up the following year, one of them would be strong enough to break the other out.
Damon won rock, paper, scissors, and he got both cups of blood. The following New Year when they were brought upstairs, as soon as Damon was let out of the cage, he attacked the doctor and pretty much everyone else at the party. However, in doing so, he managed to knock over a candelabra, which set the room on fire. When he went back to let Enzo out of the cage, he couldn't. The bars were laced with vervain and the fire was raging around him. He had to leave Enzo there. It killed him. And the only way he could deal with it was by turning off his emotions. (Do we know how long they were off after that?)
Upstairs, Aaron is pissed at Wes and ends up punching him out. He grabs some weapons and heads down to the basement. He accuses Elena of killing his parents, Megan, and his aunt. But Elena denies this. And Damon backs her up on it, because he was one who killed them (well, not Megan). He was making good on his promise to kill the whole family once he was free. Elena is shocked to discover that he killed the aunt just a few months ago when they were together, having their summer of love.
Arron ends up shooting Damon at pretty close range. But, he's a vampire, so he doesn't die or anything, but it certainly seems to hurt when he finally wakes up. He calls for Elena, but her cell is empty. Because Elena is down in the lab (or wherever this is) strapped to a table. When she wakes up, she finds a vampire strapped to a table next to her. He introduces himself as Enzo. Fuck. That means that poor Enzo didn't die in that fire. He got recaptured and has been doing this for 70 fucking years. Fuck. That sucks.
Back in Mystic Falls, Caroline is trying to help Stefan get passed his PTSD by locking him in a safe. He's in there freaking out while Caroline and Katherine argue outside. At some point, he passes out and they toss Katherine in there with him. When he comes to, she tells him not to be mad at her. Somehow she manages to calm him down (basically by telling him he's using this to replace the sadness he feels about Elena leaving him for Damon), they are just about to kiss, when Caroline pulls the safe open claiming it was too quiet and she got worried.
Once they are out, Caroline calls Elena to discuss and tell her she'll be staying at her mom's. But then, her vampire ears hear Katherine and Stefan making out (or maybe having sex, but we only see them making out) in the other room and begs Elena to call her back. Um, Elena is trapped in a secret lab that no one knows exists. I think it's gonna be a while Caroline. (We learned earlier that Damon never told Stefan about his time being tortured as he didn't want to add to his guilt).