From the back of the adventure:
Strange Things Afoot in the CityA strange visitation on the streets of Loudwater leads to the search for what's behind an ancient spectral mystery.
Key to Phantom's Cloister is an adventure for the Dungeons & Dragons (3.5 Edition)<span style="vertical-align:text-top;"><sup>®</sup></span> game. It can either be played as a stand-alone adventure, or as part of the LGR - Legacy of the Green Regent™ campaign offered by the RPGA<span style="vertical-align:text-top;"><sup>®</sup></span>. Designed to challenge 2nd-level D&D<span style="vertical-align:text-top;"><sup>®</sup></span> heroes, in this adventure they are asked to uncover what is behind an ancient and ghostly mystery.
To use this adventure, a Dungeon Master also needs the Player's Handbook (D&D 3.5e), the Dungeon Master's Guide (D&D 3.5e) and the Monster Manual (D&D 3.5e). This adventure is set in the Forgotten Realms<span style="vertical-align:text-top;"><sup>®</sup></span> game world, and it may also be useful, but not necessary, to also have a copy of the Forgotten Realms Campaign Setting.