Thunderspire Labyrinth is the second in the three part series of adventures introducing the new 4th edition Dungeons & Dragons concept of Points of Light, a loosely connected and open-ended setting designed to allow modules and Dungeon Masters created materials to be seamlessly integrated into either a single, largely unmapped fantasy world or a Dungeon Master custom made setting. The adventure, written by Mike Mearls and Richard Baker was published in 2008 by Wizards of the Coast, as a sequel to the adventure Keep on the Shadowfell. The adventure is designed for character of levels 4-6 and the module code "H" stands for Heroic Tier. This module is set in a region of the world called the Nentir Vale, the details of which are given in the 4th edition Dungeon Master's Guide.
Thunderspire Labyrinth can be run as either a loose sequel to Keep on the Shadowfell or as a standalone module.
Players find themselves journeying to Thunderspire, a mountain beneath which lies the abandoned subterranean minotaur city of Saruun Khel. The module suggests many goals for players in Saruun Khel, the largest of which is to investigate a slave ring run by a group called the Bloodreavers and rescue a group of civilians recently enslaved by this organisation. (This may be as a result of events in Keep on the Shadowfell or through other, unconnected, plot hooks.)
The players then proceed through a number of mini-dungeons; the Bloodreavers turn out to have sold the slaves to the duergar tribe known as Clan Grimmerzhul, who have then onsold a smaller subset of the slaves to a band of fiend-tainted gnolls. Finding and overcoming the gnolls reveals a sinister plan about to be enacted by a renegade wizard named Paldemar, who has designs on conquest of the Nentir Vale in which Thunderspire is located. Ultimately players confront and defeat Paldemar, which concludes the module.