From the publisher's web site:
The Dread King walks the surface world again.
An Army of Light decends upon one of the seven, and casts it into Darkness.
And the blood of thousands of unbelievers runs in rivers at the feet of he who would be a god.
Part 1: The Day of Light
Part 2: The Quest
Part 3: The Ascension
In order to play Dregoth Ascending, you will need The Dungeon Masters Guide, Player's Handbook, Monster Manual, and the Expanded Psionics Handbook, as well as the Dark Sun 3 Core rules and Terrors of Athas, available as free downloads from the official Dark Sun web site athas.org. The DM is encouraged to read The Dark Sun Revised Campaign Setting, City by the Silt Sea, Veiled Alliance and Elves of Athas. These products contain additional information the DM can use to enhance the adventure.
Dregoth Ascending is set in Free Year 12.