A small group of cannibals has started roaming farther out from their remote home and have come into contact with some farms.
The heroes find a small crypt somewhere and being brave adventurers they want to check it for evil forces (=graverobbing). Or for any other reason.
As a mage walks through the forest a sprite appears on a branch in front him (or her). The mage will be the only one that will be able to see the sprite. The sprite demands that the mage release him from the forest.
On the outskirts of a poor looking village is a large mausoleum that is well kept and richly deserted. It has a marble walkway and bricked windows with beautiful ironwork adorning it. For grave robbers the look of the outside tells of untold riches on the inside.
In a village the characters hear rumors of a man that recently came through screaming of demon attacks and murderous insects.
A large explosion was heard 4 days ago coming from the foot of the nearby mountains. Ever since then no trade wagons have come through as they usually did.
All spell casters gain their abilities through a form of demon possession. So in order to gain magical abilites, PCs must track down and trap demons. Of course there are some pretty powerful demons, if the demon is stronger than the PC, the PC could find themselves subjugated to the Demon's will.