I would love it if y'all would throw some ideas my way. I'll tell you what I have so far and highlight some particular missing pieces. Anything you come up with I can probably use somewhere. Thanks!
A ship (name?) returns from a 3-year trading and exploration voyage. Instead of docking, the ship drops anchor in the outer harbor. On investigation, a flag is spotted the meaning of which is "Plague Here." The harbor patrol sends out boats to blockade anyone from trying to visit or escape from the plague ship.
There are:
1) Families whose loved ones may or may not be alive on the ship
2) A corrupt (someone) expecting a delivery of something shocking/scandalous/illegal who is very afraid this will be discovered
3) Merchants who are "losing money every day" their goods are stuck on the ship
4) A gang of thieves who plan to sneak aboard and loot the ship, hoping that either there is no plague or else that they can pay to be cured at a temple.
5) Jittery citizens who call for the ship to be burned and sunk without delay to avoid contaminating the town/city.
The PCs might be members of or else working for any of these groups.
So here are some questions and missing details:
1) Is there really a plague? Is the flag to cover up a mutiny? Is the plague real, but secondary to the real problem on board? How did the plague start?
3) What will the town/city do to address the ship? There are magic users and a few characters with flying mounts, so someone might try to scry or do a flyover. What do they find, how can that info. get back to the PCs?
4) What really happened to the ship and its crew? How many of the crew are alive?
5) Assuming the PCs manage to get aboard, what do they find?