 He is co-author of "The Mars Mystery" (with Graham Hancock and Robert Bauval).His book "Warriors of the Wasteland" (Watkins, 2002) examined the Medieval legends of the Grail in light of Indo-European, especially Celtic, myth.His novel "Beowulf and Grendel" (Watkins, 2005) interprets "Beowulf" as "the recounting in poetic form of a religious conflict between two pagan cults in Denmark around AD 500" (p. 5).