In 1988, TSR published H4: The Throne of Bloodstone. It was written by Douglas Niles and Michael S. Dobson as the culmination to H - The Bloodstone Pass Saga, which came to be known as a high-level adventure series of modules. This module is the longest in the H-series, and like H2: The Mines of Bloodstone, it offers opportunities to use Battlesystem Fantasy Combat Supplement rules for the large-scale battles. Nonetheless, H4 provides a sufficiently flexible story to allow DMs to either use or ignore these mass combat components of the adventure. H4 consists of a 96-page story, with several maps for battle encounters and dungeon exploration through the Abyss.
This conversion guide allows DMs to run the original module with Dungeons & Dragons (5th Edition) and provides a reference sheet for encounters.
To use this conversion guide, you will need a copy of H4: The Throne of Bloodstone.