From the Introduction:
In the dying port town of Onuago, troubles deeper than the recent economic decline loom over the horizon. Baron Stieglitz has locked himself in his castle to the northeast and his captains vie for control of his lands. Children have been born with strange deformities. A mysterious cult has corrupted the priest of the logging town to the northwest. And beneath the rocky island in the bay a horror beyond imagining slumbers as though dead, dreaming of destruction and of the void.
This multi-part adventure is inspired by the work of H.P. Lovecraft. That said, the authors have worked to keep the ideas true to the realm of 3.5 d20 edition Dungeons and Dragons. These locations are not meant to derive from New England settings, think of them instead as extensions of whatever campaign world you the storyteller wish to place them in. As such, as with any roleplaying material found anywhere, feel free to modify this story as you see fit, as per your own campaign needs.
Encounter Levels: Horror of the Old Ones is a site based, event-driven d20 fantasy adventure with elements of horror, for 10th level characters. Player characters could reach 12th level by the adventure's conclusion, especially if they pursue the subplot surrounding the Baron, detailed in The Curse of Castle Stieglitz.