Wow. What a night in Mystic Falls. Let's run it down...
- Klaus showed up at school and apprehended Elena, while also breaking Tyler's neck after feeding him blood. The goal of this act was to pressure Bonnie into action to find a cure for why he could not make hybrids, lest Tyler die.
Klaus, meanwhile, stuck Elena in a gym with Stefan and compelled him to kill her after 20 minutes. Stefan tried to fight and when the buzzer went off he told Elena to run. He really tried to resist and he succeeded, actually snapping a broom handle to kill himself with - until Klaus intervened, compelled Stefan deeply again and seemed to eliminate all human elements from him.
At this, Stefan attacked Elena.
- But Klaus realized something: he didn't need the Doppleganger dead. He needed her blood. The Original Witch misled him. As an experiment, Klaus stopped Stefan from killed Elena and fed her blood to Tyler. It revived him and made him feel more alive - i.e. like a hybrid - than ever before. He bounded away happily with Caroline.
Klaus then placed Elena in the hospital to drain more of her blood, but Damon finally came to her rescue. He had been off with Katherine, but received texts from Bonnie and came as quickly as he could. In the time away, he learned - via Jeremy, who summoned Anna, who was told this information by Pearl - that a vampire named Michael actually hunted other vampires and was after Klaus. He was also entombed.
But Damon leveraged this information to avoid being killed by Klaus. He then got Elena out of the hospital and brought her home and swore never to leave her... but then Stefan showed up, acted like a jerk, said Klaus was gone for a bit and he was placed in charge of Elena's safety.
- Elsewhere, Matt drowned himself in order to have Elena revive him, which enabled him to finally communicate with Vicki.
- Finally, Katherine and Jeremy broke into Michael's tomb, opened up his coffin and his eyes snapped open to end the episode.