Thieves' Highway

From publisher blurb:

After spending the night in the ducal keep as a reward for a job well done, you anticipate a glorious morning. A sound of crashing stone and the smell of burning wood give you pause to think something else is going on. The town is under attack by humanoid forces and the duchess and her retinue barge in. You have been requested to come up with a solution as the military's ability to hold is waning. Rumor has it a thief in the dungeon may know a way to get behind the raiders...

This adventure setting was designed for 5th Edition rules for the Filbar Campaign for six, mid (4th) level adventurers and DM.