Hordes of Dragonspear, 2nd Edition (Advanced Dungeons & Dragons / Forgotten Realms, Module FRQ2)

Dragonspear Castle. All who live within several hundred miles have heard the bame and know its import. Once home to the proud and the brave, it stands now a ruin, cloaked behind a history of murder and diabolic plots. Few go there, for the only reward to be found is death.
Rumors abound that Dragonspear holds a portal to the sinister planes, but until now those have been unfounded. Following a great battle against orcs and trolls from the High Moor who had taken possession of the castle, a temple to ward against further evil was established. However, by the Time of Troubles, that temple and its clergy had disappeared. Now, a horde of fiends and monsters has amassed at Dragonspear Castle, and is terrorizing the surrounding countryside.
The portal is active, that is for certain. The army of Daggerford needs reinforcements! Is your party made of the stuff of heroes?