Zarkon: Lord of the Unknown in Invisible Death

Doubleday, 1975, first edition hardcover with dustjacket. This is the second in the "Zarkon" series of pulp adventure novels modeled after "Doc Savage." Other novels in the series are: "The Nemesis of Evil" (1975); "The Volcano Ogre" (1976); "The Earth-Shaker" (1982) and "Horror Wears Blue" (1987).