From the introduction:
The party has either just come to Sulindal or was there when the yuan-ti army first showed up. The invaders were in possession of a map indicating the vault’s entrance, but needed the university's scholars to decode it. The rumor is that they’ve succeeded, and have begun launching daily expeditions to the vault.
City leaders now hold secret meetings to figure out how to thwart the enemy’s efforts. Somehow, they come into contact with the PCs and implore them for help.
An adventure for 5th level characters