The Adventure Seed
A secret government organization has taken the principles behind the Global Consciousness Project and expanded it, extending both the time the Project is capable of predicting and providing information where the disturbances are likely to appear.
One major upcoming disturbance seems to be centered on the former town of Centralia on Halloween, and the PCs are sent to investigate and possibly stop it. When they do so, they discover that a coven of psychics/magicians is intending to use the time and place to summon entities of fire.
Any backup the PCs might bring is quickly overwhelmed by gouts of flame breaking through the Earth. It is up to the PCs to fight the coven, and stop the entities from running amok in the surrounding countryside - and all this in a ghost town with very unstable ground and a vast underground fire.