SettingHeshamoketh has a similar beginning to the core setting in the D&D rulebooks. The world was created by Primordials who shifted the dark parts to one side (creating the Shadowfell) and the bright parts to another (creating the Feywild). The Gods residing in the Astral Plane decided to end the chaos the Primordials inflicted upon the world and the war began to rage. In the end, the Primordials lost, and the chaos was washed away to form the Elemental Chaos plane. The Gods shaped and created the new world to their liking, and things were normal for many centuries.
Eventually, however, the Plague arrived and everything changed. Stories differ on where the Plague originated from(Zehir and the Yaunti, Tharizdun the Chained One, a Primordeal such as Murgremir- The Rotting Hill or Bwimb- Baron of Ooze), who the first carrier(s) was/were. But what is known for sure is that there was no cure and it spread fast. It was only a matter of weeks before it became an epidemic and people began to panic. Prayers went unanswered, rituals failed, herbs and medicines had no power. The storys say that Pelor himself came down to stop the spread of the Plague. Even he could not cure it and eventually, the toll of working in the mortal world among those contaminated with the vile Plague corrupted even him. Somehow, a God had caught the Plague, and was destroyed by it. Anyone found to be tainted from the Plague was cast out of the cities. However, it was not long before the wilds were consumed with the disease. Animals could no longer be hunted for fear they were carrying the disease, farmlands became unsafe to work as crazed animals or monsters that carried Plague would rampage through the cities. Supplies ran low and it became apparent there was only one option: a mass exodus of the survivors. Mages and clerics used their powers to open gateways and the people fled to the mirror planes that surrounded Heshamoketh.
Many centuries have passed, and the peoples have settled into the mirror planes (Feywild, Shadowfell, Elemental Chaos) making their homes. Trade and travel are common between the planes, though the journey can be dangerous or expensive depending on the method of travel. Though they live in peace, most of the races cannot forget the lands of Heshamoketh and once every five years an expedition is gathered and sent to determine the state of the lands. Only the bravest volunteer, as the survival rate is extremely low. The tales that do make it back speak of a world of terror. Somethings have adapted to live in the poisonous air, mostly those immune to poison or disease, and now they rule the wilds that have overrun almost every trace of civilization.