The Sunless Garden (D20)

From the cover: After arriving at a seemingly abandoned trading post, the heroes discover to their horror that all the inhabitants have been transformed into black trees! Upon further investigation, they find clues that lead them to the hidden lair of Nockmort, a treant gone bad. Nockmort has been transformed by the strange radiation of a meteorite he discovered, and now he is a terrible force of evil. The characters must enter his sunless garden to save the town. And along the way they just might discover fabulous treasure...