Undermountain: Halaster's Lost Apprentice (2010)

(from the back of the book)
Uncover a Hidden Legacy

A lost passageway on the upper level of the most infamous dungeon in Faerun has recently been uncovered. When a patron hires a band of adventurers to brave the dangers of Undermountain, a search is on to uncover secrets of an apprentice of the dungeon's lost creator - Halaster.

Undermountain: Halaster's Lost Apprentice is designed for five characters of 1st level and is the spring 2010 season of the D&D Encounters official play program. This Dungeons & Dragons adventure includes two full-color battle maps, ready-to-play encounters, and DM information on the D&D Encounters official play program.