From publisher blurb:
The dwarves of Karn Ungil seek to reclaim their former outpost of Ballo Dar from drow invaders. They are sending a small group of spellcasters to sneak into the heart of the outpost and reawaken its magical defenses. The dwarves of Karn Ungil ask the player characters to escort this expedition through the twisting tunnels of the Underdark. While drow attack the group, they face a greater danger. One of them has already betrayed the group from within.
Beacon in the Dark is an adventure for characters level 11-13. It is set in the Underdark, and can be dropped into nearly any campaign or run as a one-shot.
If features
2 Combat Encounters (including defending a besieged fortress)
1 Skill Encounter
9 New Monsters
1 New Magic Item