Shadows of Madness (Pathfinder)

From publisher blurb:

For 4-6 Characters of Levels 6-7

Many years ago Tibor, a wizard with an overwhelming desire for knowledge of the plane of shadow, locked himself away in a tower to pursue his studies.

Shortly thereafter, his tower was consumed in a dark explosion, and the mage was assumed dead. However, assumption can never be taken as fact, and now the PCs have stumbled upon a hidden stairway where the tower once stood, leading down into the shadowy earth below...