All I had to do was kill two vamps and the quest updated: "Talk to Eltrys." Okay, where is he? At the bottom of a ramp was a partially submerged cage with a body floating inside. Guess who? Yep, and then I remembered: he was murdered by the Markarth guards in the Temple of Talos during the Forsworn Conspiracy. Nice. He's long dead, yet is kidnapped by vampires and hauled halfway across Skyrim for me to rescue.
Fortunately I'm on a PC and can manually advance the quest to completion, but I can see how our console playing friends will eventually have a clogged journal. Very frustrating.
