From back cover:
The new MEGA-ADVENTURE by Monte Cook...takes characters from 6th to 10th level.
Long ago, a powerful saint gathered dozens of the world's most malignant fores of evil and locked them away in his far-flung warrens behind magically seal doors.
Today someone opened a door...
This adventure is set in the Ptolus campaign setting, even though it was published before it. A PDF copy of the adventure was included on the CD that came with the hardcover version of Ptolus: Monte Cook's City by the Spire.