The story follows survivors dealing with a pandemic that causes its victims to carry out their most evil thoughts. Carriers of the virus are generally known as the “Crossed” due to a large, cross-like rash that appears on their faces – other names include “cross-faces” and “plus-faces”. This contagion is primarily spread through bodily fluids, which the Crossed have used to great effect by treating their weapons with their fluids, as well as through other forms of direct fluidic contact such as rape and bites, assuming the victim lives long enough to turn. A major difference between the Crossed and other fictional zombie or insanity-virus epidemics (e.g., in the film 28 Days Later) is that while the Crossed are turned into homicidal violent psychopaths, they still retain a basic human-level of intelligence: thus, they are still capable of using tools and weapons, driving motor vehicles, setting complex traps, and other actions. It is occasionally noted in the series that a Crossed retains any skills they had prior to their infection; most simply lack the patience or sanity to do anything not immediately related to their vicious impulses.
