From the back cover:
"The end times approach...
To everything there is a season. Every campaign has to come to and end sometime, so why not go out with a bang? The Apocalypse Stone is an epic adventure to challenge high-level characters, but beware - it will destroy your world!
This adventure has it all: gods and devils, plague and pestilence, rains of fire, and world-shattering conflicts. Here is an opportunity for PCs to display undreamt-of heroism...or fall to ultimate defeat.
The Apocalypse Stone is a tool for Dungeon Masters to present extremely challenging encounters for high-level parties, to wrap up a long-running campaign...or both.
This adventure can be used with your own game world or any ADVANCED DUNGEONS & DRAGONS setting."