The Crimson Horde by Jeff Cooke

Elder cross, a city much like your own, seemingly safe and secure, is about to be consumed by a nightmare of crimson hue. A mist, unnatural and terrifying, rolls in from the horizon, bringing with it not the slow, shambling undead of countless other stories, but something far more sinister. These are creatures of adaptation, of evolving horror, driven by an intelligence that chills to the bone.