Tessa essentially kills Silas, rotting him away from the inside and rendering him helpless. But this is a problem because Damon had made a deal that when Silas got the cure and turned into a witch in order to die... he'd trade his life for Bonnie's.
So Damon invited Katherine over to take a look at the nearly dead Silas, only to feed her to him in the hopes it would help his plan. Silas DID drink all of Katherine's blood... but the episode ended with her still alive and asking, "Am I in Hell?"
Oh, and Nadia revealed that she is Katherine's daughter. So there's that.
Elsewhere: Dr. Maxfield is using Jesse as a vampire subject, but we don't know why. He's also the legal guardian of a mysterious student named Aaron who knew Megan.
And he also warned Elena that people are watching her at Whitmore.
Finally, Tyler broke up with Caroline so he could go take care of Klaus.