Angels or Demons? The grey is fading. GREY KNIGHTS is Rachel DeFriez’s chilling sequel to GREY MATTERS. The Z-Virus has mutated and the infection looms large on the Texas horizon. As the rushing tide of the apocalypse smears the lines between heaven and hell, Evelyn and Greyson escape the fire of one quarantine zone, only to find themselves fugitives in the inferno of another.