When investigating Xanathar, I ended up getting caught. I'm not sure by whom, but I hadn't made it far into the base before I was struck from behind and fell unconscious. I will have to review with Gipels how precisely to use his pendant properly... or maybe not, since it seems they took it, and it'd be best if he forgot about it.
Upon coming to, I found myself in an arena where, surprisingly, I found myself face to face with Xanathar after defeating many opponents, though I hadn't realized it at the time. An ugly bastard, that one; a powerful one though, given he was a beholder. Upon defeating my last opponents, I made my escape, not wanting the (presumed) corrupt power he had offered upon success. I soon ran into a surprisingly diverse group of six adventurers who appeared to be ransacking Xanathar's lair.