From the front of book:
Rumors of an alliance between the Council of Blades in Mulmaster and a group of Banite Warlock Knights of Vaasa portend evil for the entire Moonsea region. Two years ago, a great earthquake rattled northern Vaasa and Damara. The ruined Castle Perilous sloughed off crumbling stone and the marks of age, revealing a sleek and dark edifice beneath, covered with shimmering black runes of unknown purpose. A powerful Warlock Knight now attempts to breach the castle's defenses, and your patron fears that his efforts will succeed. You must unlock the castle's secrets before the merciless lords of tyranny gain access to the ancient and terrible powers of the Witch-King Zhengyi.
A Living Forgotten Realms Special adventure set in Vaasa for characters levels 17-20.