Eirth is an alternate version of Earth, with similar people, places, and problems. However, it is much darker than our own world, and there are far more monsters and things that go bump in the night.
Humanity is alone in the world. The other mortal races have been completely erased from existence. The gods are dead, and magic has disappeared from the lives of men. Civilization has been reduced to ashes, and mankind has been driven into the darkness of caves.
Humanity is resilient though, and time marches forward. With magic gone, humanity has embraced technology. Stone has given way to bronze, bronze has given way to iron, and iron has given way to steel. Humanity has had a dark ages, followed by a renaissance. An industrial revolution brought steam and assembly lines, and now computers and the internet have connected humanity, while weapons of mass destruction threaten to tear us apart.
Beneath the glow of artificial lights and cell phone screens, humanity feels safe. However, deep within the darkness, an ancient evil has awakened. Striking from the shadows, it picks off humanity one by one, and builds an army hell-bent on destruction.