OOC:
It's been a while, so I might have a few details mixed up or mistaken. We do know that the Cult of the Dragon is doing something with all the loot, and we found out that they're taking it to a castle (I think Xalana read someone's mind for that piece of information).
Lennithon the Blue (a dragon that asked us to recover her egg from the hatchery near Greenrest) told us about Rezmir, whom I believe is a woman that wears purple. I think Rezmir is leading all of this, but I don't recall if we ever met or saw her in person.
As for the worship of Tiamat, I think we all inferred that with how fanatical the cultists were. Even Lennithon was unwilling to cross Tiamat, despite her indifference to our conflicts with the cult.