When Morgan le Fay (Morgaine) has to sacrifice her virginity during fertility rites, the man who impregnates her is her younger brother Arthur, whom she turns against when she thinks he has betrayed the old religion of Avalon.
Three different generations of holy women of Avalon; Caillean, Dierna, and Ana, struggle to guide the fortunes of Roman Britain and their own destinies in the years before the birth of the legendary King Arthur.