The king is having a new wine celler dug when they find a ancient opening to a hidden dungeon. The king sent his head guard, the local wizard, and some handpicked royal guards to investigate. That was four days ago and still nobody emerged. He then sent in a few more guards to find out what happened and they came out with the dead wizard as well as most of the original royal guards.
Fearing to loose more of his faithfuls he hires some local adventurers to do the dirty work.
1) The head guard could be corrupt. They found a large stash of money/magic left by previous era or perhaps it was once the basement of a rich church. Local clergy may know. Either way it is obvious that the tracks show a great deal of things being taken from a room and out a different path. Find the loot or tell the king…or both.
2) The head guard found the stash but released a great demon that destroyed his group in the process. Now the demon is free and trying to release other demons that were trapped in the same situation. The demon was released on accident and the head gueard doesn’t know how he did it. The demon keeps him alive and tries to find out anyway.