A One-Round Living Greyhawk Highfolk Regional Adventure
From the introduction:
After many long weeks under a magical dome of twilight, effectively crippling the forest town of Quaalsten, a breakthrough has been made. Now, you must journey to a place beyond reality to bring down the baleful sorcery that prevents the forces of good from turning the tide.
Recommended for characters levels 1-13.
Blood on the Trees, Part 2.