Some time around the 2030s, the Earth is ravaged by a string of viruses after a corporate cargo ship, returning from an orbital lab, crashes into the atmosphere. Vast numbers of people die. Some are left altered by the pathogen, visibly changed on a molecular level. Others are affected in a more horrific way: turned into the living dead, unable to die without violence, locked in a state of perpetual fury, and with an infectious bite, they force most cities to be left abandoned. The event was called Yellow Dawn. Ten years on, and civilisation has rebuilt itself. It is this new world into which the players venture out.
Those changed by the virus devolved into one of two states. Those altered horrifically in terms of looks, but better suited to adapt to the wilderness are known, unfairly, as orcs, looking much the part of the grotesque dark skinned creatures made famous from the Lord of the Rings trilogy. Those who remained human on the outside but became psychotic monsters are known as zombies, much in the style of those made popular by 28 Days Later. Also, very ocassionally, you might find the robots - when the virus first appeared their response was to slaughter the infected, since then they appear to have pretty much disappeared.
Within the few cities that have survived the collapse of society intact, life goes on, pretty much as before but with fewer resources. Immediately outside the walls, and lurking in the shells of other once proud cities, vast numbers of zombies can be found. And it the wilderness between cities live those brave enough to make a living from the world around them, including the tribes of orcs that have banded together for self-preservation.
And deeper in the shadows lurk all sorts of horrible inhuman creatures... angels, demons and things man was not supposed to know...
Given the title of the game, and its subtitle, you'd think so, wouldn't you? And whilst the game system is very much built around the bones of the system used in The Call of Cthulhu RPG and mentions that The Cthulhu Mythos and its agents are alive and well (especially in a climate that fosters isolated communities), the section actually granted to such entities is very brief. Still, given the title of the game and the fact that there are mythos references at all hints at perhaps something to come further into the game's development.
After the initial version of the game David J Rodger himself updated the game to contain more details of how the mythos can be employed in the game, through various entities and artifacts, and promises: "I'm currently working on a major campaign, "Shadows of the Quantinex" that reveals the actual Mythos plot behind Yellow Dawn, and what is scheduled to happen next - unless those pesky investigators can stop it. They're not finished with humanity yet."
In Feburary 2012, the 2.5 Version of Yellow Dawn was released. This new version expanded on Hastur's influence on the world, "something which was considered lacking in the previous version of the rulebook." It turns out the "zombies" are really the manifestation of Hastur on reality:
"The term zombies is actually a misnomer, created by the survivors and emerging popular media after Yellow Dawn happened...
"The truth is. Well, the truth is revealed in the campaign book "Shadows of the Quantinex", but the over-arching
principle is that the essence of Hastur has infected these people. They’re lost in a never-ending existence of horror and rage. Their existential reality now overlaps with a slithering, confusing, non-Euclidean, ever-shifting meta-reality where they are in thrall to the entity / concept / meme that is the King in Yellow." - From "About Yellow Dawn" by David J. Rodger.
As stated before, the game system is based very much upon that used with the Call of Cthulhu RPG. However, David J Rodger has built upon this, adding the idea of Ranks to professions (somewhat like Class Levels in Dungeons & Dragons) that represent conviction and faith in your own abilities combined with the respect granted to you through exercising this conviction. Furthermore, there are rules and tables for all sorts of situations. Whilst it might be disappointing to find little mention of The Hastur Mythos within compared with the amount devoted to the post-apocalyptic world filled with zombies and mutants, the system and setting itself are amazingly well-developed.