From the publishers blurb:
The Horsemen of Reinhorn is an adventure and town setting designed for use with Old School Essentials Advanced Fantasy. It can be used with Old School Essentials Classic Fantasy with minor changes to the NPCs and adversaries used in the module. Retainers are encouraged.
We’ve placed all the maps in a separate Map Pack for ease of importing the maps into a virtual table top or printing maps for your individual needs.
This adventure begins with the arrival of the characters to the dwindling town of Reinhorn situated at the edge of the kingdom and part of a barony that the denizens of the realm consider cursed. The characters learn of Reinhorn’s dirty secrets and curse, ghostly horsemen who steal children for their dread mistress.
This information propels the characters through the wilderness against a band of brigands, and eventually to Iron Pike Castle. The castle is masked with illusions which the characters must overcome when they first arrive.
Once the PCs venture into the castle, they face numerous horrors including the tormented souls of the kidnapped children who haunt the halls of Iron Pike Castle. The castle’s denizens are bound to the baroness who rules ruthlessly. Those that enter her castle in attempt to liberate the stolen children and fail, join her ghastly minions.
Should the characters prevail through their exploration of the castle, they face the Horsemen again and have a final confrontation with the baroness.
The main locations for the module are described in the accompanying map pack.