What are the Dragon Cult Plotting?

18 Flamerule, 1486 DR - The Cult of the Dragon, alongside kobolds and a blue dragon attack Greenest.

Why did the attack occur? Who is the dragon? Is this part of a larger attack?

- Information gathered during the attack gives us insight into the motives of the cult. They spent most of the time gathering a "horde." - Interogation of cultist had us learn that other attacks may occur around the Sword Coast, and that some sort of plot is in action.   19 Flamerule, 1486 DR - The raiders departed Greenest.