The PCs are approached by a dwarven woman named Baera, who asks them to investigate the Weeping Willow Tavern. It opened only a few months ago and is always full of people for no obvious reason. Baera runs a tavern on the same street and finds this suspicious.
The proprietor of the Weeping Willow Tavern, Tael Blackjaw, is actually a young dragon who’s using charm magic to attract customers to the tavern, but for a purpose well beyond ordinary commerce.
As a friendly faction, Tael is a silver dragon who’s tracked an aboleth (or similar mind-controlling creature) to this city. It appears to be after something belonging to a spellcaster named Tarin Silvertongue, but it’s thoroughly covering its tracks.
Every evening, Tael takes one or two charmed patrons downstairs to the basement, where he’s set up a zone of truth that will remain for the next 30 days. He then questions the patron about anything unusual or suspicious they’ve seen recently, looking for evidence of mind control. Afterwards, he harmlessly erases the patrons’ memories of their questioning and returns them to the taproom, none the worse for wear.
Tael has plenty of uses for a sympathetic party of PCs, and will gladly hire them to follow up on reports of suspicious activity.
As a foe faction, Tael is a black dragon whose real goal is to stock his swamp cave lair with stirges. He’s doing so in a remarkably evil way: He keeps a dozen stirges in a secret room in the tavern’s basement, and every evening takes one or two charmed patrons downstairs and has the stirges feed on them, just before the point where the victims’ blood loss would be obvious to others. He then magically erases the patrons’ memories and returns them upstairs.
The basement itself contains a teleportation circle that will last for the next 30 days, and magic runes on the floor, just barely visible if you’re keeping a keen eye out. Stepping on a rune magically alerts Tael of intruders.
If the PCs figure out what Tael’s doing and attempt to expose him, he’ll teleport the stirges back to his cave and retreat, periodically sending assassins after the PCs just out of spite.