He said John was full of crap because Katherine was BFFs with Pearl. If he truly knew Katherine, he'd be aware of this fact - from there, Damon kicked John out of the house and said he'd kill every member of the Founder's Council if John said anything to them about his identity.
As he dealt with all this information, Damon also discovered why the local blood banks were dry: Stefan robbed them. Dude has a serious drinking problem and he's lying to Elena about it. Damon tries to talk sense into his brother and tries to keep this information to himself, but it's all too much for him to handle. At the Miss Mystic Falls pageant, where Caroline and Elena are among the women competing, Damon tattles on Stefan right in front of him.
He then goes downstairs for a drink, while Stefan tries to tell Elena he's fine. But isn't having it. Stefan leaves in a huff and runs into Amber, another pageant contestant. He compels her and takes her outside and then into the woods. He's trying to fight it, but Stefan is starving. He's hooked on blood. He actually bites into her neck, as viewers wonder if he'll actually kill her.
While this is taking place, Elena and Damon are bonding at the pageant because the latter has taken over as the former's date. They share a nice dance, but soon realize Amber is missing. Running into the woods, they find Stefan feeding on her. They try to yell at him, but only Bonnie - who returned this week, unable to be friends with Elena because she holds the Salvatores responsible for Gram's death - can do so by using her witch powers.
Stefan runs home, a bloody, ashamed mess.
Elena follows and says she can help him through this, but Stefan is angry. He says the blood has simply brought out his true self and Elena should just leave him alone. But she doesn't scare easily. Elena manages to get close to Stefan and hug him - and then inject him with a vervain-filled dart. Damon walks in and carries Stefan into the basement. He gets locked in, as Damon and Elena sit outside, hoping this detox works.
In other storyline news: Anna and Jeremy grew closer, as the latter told the former what he knew from Elena's diary; and Anna admitted she had feelings for Jeremy. Anna also tells Damon all vampires from her house, except Harper, have been kicked out and are gone.
Pearl also comes around, telling Damon she wants to remain in Mystic Falls because her daughter is happy there. As a peace offering, she gives Damon something; an invention John Gilbert made. Pearl stole it awhile ago, thinking it was the vampire-finder John created. But that was something different. Pearl has no idea what this small invention actually does, and we're left to wonder: Is this what Uncle John Gilbert is after?
Source: TV Fanatic